---
title: 'GenomicTuples: Classes and Methods'
author: "Peter Hickey"
date: "Modified: 12 February 2015. Compiled: `r format(Sys.Date(), '%d %b %Y')`"
output: 
  BiocStyle::html_document:
    toc: true
vignette: >
  %\VignetteIndexEntry{GenomicTuplesIntroduction}
  %\VignetteEngine{knitr::rmarkdown}
  \usepackage[utf8]{inputenc}
---

```{r style, echo = FALSE, results = 'asis'}
BiocStyle::markdown()
```

```{r, echo = FALSE}
knitr::opts_chunk$set(collapse = TRUE, comment = "#>")
```

# Introduction

The `r Biocpkg("GenomicTuples")` R package defines general purpose containers
for storing _genomic tuples_. It aims to provide functionality for
tuples of genomic co-ordinates that are analogous to those available for
genomic ranges in the `r Biocpkg("GenomicRanges")` Bioconductor package.

As you will see, the functionality of the `r Biocpkg("GenomicTuples")` package
is based almost entirely on the wonderful `r Biocpkg("GenomicRanges")`
package. Therefore, I have tried to keep the user interface as similar
as possible. This vignette is also heavily based on the vignette "An
Introduction to Genomic Ranges Classes", which is included with the 
`r Biocpkg("GenomicRanges")` package[^GenomicRanges]. While not essential, familiarity with the `r Biocpkg("GenomicRanges")` will be of benifit in understanding the `r Biocpkg("GenomicTuples")` package.

[^GenomicRanges]: The `r Biocpkg("GenomicRanges")` vignette can be accessed 
by typing` vignette("GenomicRangesIntroduction", package = "GenomicRanges")` at the R console.

## What is a genomic tuple?

A genomic tuple is defined by a _sequence name_ (`seqnames`), a 
_strand_ (`strand`) and a _tuple_ (`tuples`). All positions 
in a genomic tuple must be on the same strand and sorted in ascending order. 
Each tuple has an associated `size`, which is a positive integer. For example, 
`chr1:+:{34, 39, 60}` is a 3-tuple (`size` = 3) of the 
positions `chr1:34`, `chr1:39` and `chr1:60` on the 
`+` strand.

When referring to genomic tuples of a general (fixed) `size`, I
will abbreviate these to $m$-tuples, where $m$ = `size`. I
will refer to the first position as $pos_{1}$ (`pos1`), the second
as $pos_{2}$ (`pos2`), $\ldots{}$, and the final position as
$pos_{m}$ (`posm`).

The difference between a genomic tuple and a genomic range can be
thought of as the difference between a set and an interval. For example,
the genomic tuple `chr10:-:{800, 900}` only includes the
positions `chr10:-:800` and `chr10:-:900` whereas the
genomic range `chr10:-:[800, 900]` includes the positions
`chr10:-:800`, `chr10:-:801`, `chr10:-:802`,
$\ldots{}$, `chr10:-:900`.

## When might you need a genomic tuple?

In short, whenever the co-ordinates of your genomic data are better defined by 
a set than by an interval.

The original use case for the _GTuples_ class was to 
store the genomic co-ordinates of "methylation patterns". I am currently 
developing these ideas in a separate R package, 
`r Githubpkg("PeteHaitch/MethylationTuples")`, which makes heavy use of the 
_GTuples_ class. Other genomic data, such as long reads containing 
multiple variants, may also be better conceptualised as genomic tuples rather 
than as genomic ranges and therefore may benefit from the 
`r Biocpkg("GenomicTuples")` infrastructure.

# _GTuples_

The _GTuples_ class represents a collection of genomic tuples,
where each tuple has the same `size`. These objects can be
created by using the `GTuples` constructor function. For example, the following 
code creates a _GTuples_ object with 10 genomic tuples:

```{r initialize, echo = TRUE, eval = TRUE}
library(GenomicTuples)
```

```{r example-GTuples, echo = TRUE, eval = TRUE}
seqinfo <- Seqinfo(paste0("chr", 1:3), c(1000, 2000, 1500), NA, "mock1")
gt3 <- GTuples(seqnames = Rle(c("chr1", "chr2", "chr1", "chr3"),
                              c(1, 3, 2, 4)),
               tuples = matrix(c(1:10, 2:11, 3:12), ncol = 3),
               strand = Rle(strand(c("-", "+", "*", "+", "-")),
                            c(1, 2, 2, 3, 2)),
               score = 1:10, GC = seq(1, 0, length = 10), seqinfo = seqinfo)
names(gt3) <- letters[1:10]
gt3
```

The output of the _GTuples_ `show` method is very similar to that of the `show`
method for _GenomicRanges::GRanges_ objects. Namely, it separates
the information into a left and right hand region that are separated by
`|` symbols. The genomic coordinates (`seqnames`,
`tuples`, and `strand`) are located on the
left-hand side and the metadata columns (annotation) are located on the
right. For this example, the metadata is comprised of `score` and
`GC` information, but almost anything can be stored in the
metadata portion of a _GTuples_ object.

The main difference between a _GTuples_ object and
_GenomicRanges::GRanges_ object is that the former uses _tuples_
while the latter uses _ranges_ in the genomic coordinates.

For even more information on the _GTuples_ class, be sure to
consult the documentation:

```{r GTuples-help, eval = FALSE, echo = TRUE}
?GTuples
```

## _GTuples_ methods

Most methods defined for _GenomicRanges::GRanges_ are also
defined for _GTuples_. Those that are not yet defined, which
are those that make sense for ranges but generally not for tuples,
return error messages.

If you require a method that is not defined for _GTuples_ but is defined 
for _GenomicRanges::GRanges_, then this can be achieved by first 
coercing the _GTuples_ object to a _GenomicRanges::GRanges_ object; 
__Warning: coercing a _GTuples_ object to a _GenomicRanges::GRanges_ is generally a destructive operation__.

```{r GTuples-coercion, eval = TRUE, echo = TRUE}
as(gt3, "GRanges")
```

### Basic _GTuples_ accessors

The components of the genomic coordinates within a _GTuples_
object can be extracted using the `seqnames`,
`tuples`, and `strand` accessor functions.
__Warning: The `tuples` accessor should be used in place of the `ranges` accessor. While the `ranges` method is well-defined, namely it accesses $pos_{1}$ and $pos_{m}$ of the object, this is not generally what is desired or required.__

```{r GTuples-accessors1, eval = TRUE, echo = TRUE}
seqnames(gt3)
tuples(gt3)
strand(gt3)
```

Stored annotations for these coordinates can be extracted as a
_DataFrame_ object using the `mcols` accessor:

```{r GTuples-accessors2, eval = TRUE, echo = TRUE}
mcols(gt3)
```

_Seqinfo_ can be extracted using the `seqinfo` accessor:

```{r GTuples-accessors3, eval = TRUE, echo = TRUE}
seqinfo(gt3)
```

Methods for accessing the length and names are also defined:

```{r GTuples-accessors4, eval = TRUE, echo = TRUE}
length(gt3)
names(gt3)
```

### Splitting and combining _GTuples_ objects}

_GTuples_ objects can be divided into groups using the
`split` method. This produces a _GTuplesList_ object, a
class that will be discussed in detail in the next section:

```{r split, eval = TRUE, echo = TRUE}
sp <- split(gt3, rep(1:2, each=5))
sp
```

If you then grab the components of this `GenomicTuplesList`, they can also be 
combined by using the `c` and `append` methods:

```{r c, eval = TRUE, echo = TRUE}
c(sp[[1]], sp[[2]])
```

### Subsetting _GTuples_ objects

The expected subsetting operations are also available for
_GTuples_ objects:

```{r subsetting-GTuples1, eval = TRUE, echo = TRUE}
gt3[2:3]
```

A second argument to the `[` subset operator can be used to
specify which metadata columns to extract from the _GTuples_
object. For example:

```{r subsetting-GTuples2, eval = TRUE, echo = TRUE}
gt3[2:3, "GC"]
```

You can also assign into elements of the _GTuples_ object. Here
is an example where the 2nd row of a _GTuples_ object is replaced
with the 1st row of `gt3`:

```{r subsetting-GTuples3, eval = TRUE, echo = TRUE}
gt3_mod <- gt3
gt3_mod[2] <- gt3[1]
head(gt3_mod, n = 3)
```

There are also methods to repeat, reverse, or select specific portions
of _GTuples_ objects:

```{r subsetting-GTuples4, eval = TRUE, echo = TRUE}
rep(gt3[2], times = 3)
rev(gt3)
head(gt3, n = 2)
tail(gt3, n = 2)
window(gt3, start = 2, end = 4)
```

### Basic tuple operations for _GTuples_ objects

Basic tuple characteristics of _GTuples_ objects can be extracted
using the `start`, `end`, and `tuples` methods.
__Warning: While the `width` method is well-defined, namely as $pos_{m} - pos_{1} + 1$, this may not be what is required. Instead, please see the `IPD` method that will be discussed in the next section__.

```{r tuple-operations, eval = TRUE, echo = TRUE}
start(gt3)
end(gt3)
tuples(gt3)
```

#### Intra-tuple operations

Most of the intra-range methods defined for
_GenomicRanges::GRanges_ objects are not currently defined via extension 
for _GTuples_ objects due to the differences between _ranges_ and
_tuples_. Those not currently defined, and which return an error message,
are:

- `narrow`
- `flank`
- `promoters`
- `resize`
- `Ops`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

Both the `trim` and `shift` methods are well-defined,
although the former is somewhat limited since it will return an error if
the _internal positions_ exceed the `seqlengths`:

```{r shift, eval = TRUE, echo = TRUE}
shift(gt3, 500)
```

```{r hift-error, eval = TRUE, echo = TRUE, warning = TRUE, error = TRUE, purl = FALSE}
# Raises warning due to tuple being outside of seqlength
x <- shift(gt3[1], 999)
x

# Returns an error because internal position exceeds sequence length, resulting 
# in a malformed tuple when trimmed.
trim(x)
```

#### Inter-tuple operations

None of the inter-range methods defined for
_GenomicRanges::GRanges_ objects are currently defined via extension for
_GTuples_ objects due to the differences between _ranges_ and
_tuples_. Those not currently defined, and which return an error message,
are:

- `range`
- `reduce`
- `gaps`
- `disjoin`
- `isDisjoint`
- `disjointBins`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

#### Interval set operations for _GTuples_ objects

None of the interval set operations defined for
_GenomicRanges::GRanges_ objects are currently defined via extension for
_GTuples_ objects due to the differences between ranges and
tuples. Those not currently defined, and which return an error message,
are:

- `union`
- `intersect`
- `setdiff`
- `punion`
- `pintersect`
- `psetdiff`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

### Additional methods unique to _GTuples_

_GTuples_ have a few specifically defined methods that do not
exist for _GenomicRanges::GRanges_. These are `tuples`,
`size` and `IPD`.

The `tuples` method we have already seen and is somewhat
analagous to the `ranges` method for
_GenomicRanges::GRanges_, although returning an integer matrix
rather than an _IRanges::IRanges_ object:

```{r tuples-method, eval = TRUE, echo = TRUE}
tuples(gt3)
```

The `size` method returns the size of the tuples stored in the
object:

```{r size-method, eval = TRUE, echo = TRUE}
size(gt3)
```

Every m-tuple with $m \geq 2$ has an associated vector of intra-pair
distances ($IPD$). This is defined as
$IPD = (pos_{2} - pos_{1}, \ldots, pos_{m} - pos_{m - 1})$. The
`IPD` method returns this as an integer matrix, where the $i^{th}$ 
row contains the $IPD$ for the $i^{th}$ tuple:

```{r IPD-method, eval = TRUE, echo = TRUE}
IPD(gt3)
```

## Implementation details

While the _GTuples_ class can be thought of as a matrix-link
object, with the number of columns equal to the `size` of the
tuples plus two (one for the `seqname` and one for the
`strand`), internally, it extends the _GenomicRanges::GRanges_
class. Specifically, the `ranges` slot stores an
_IRanges::IRanges_ object containing $pos_{1}$ and $pos_{m}$ and,
if `size` $> 2$, a matrix is used to store the co-ordinates of the  "internal 
positions", $pos_{2}, \ldots, pos_{m - 1}$ in the `internalPos` slot. If
`size` $\leq 2$ then the `internalPos` slot is set to `NULL`. The 
`size` is stored as an integer in the `size` slot.

While there are arguments for creating stand-alone _GTuples_ and
_GTuplesList_ classes, by extending the _GenomicRanges::GRanges_ and
_GenomicRanges::GRangesList_ classes we get a lot of very useful functionality
"for free" via appropriately defined inheritance.

# _GTuplesList_

The _GTuplesList_ class is a container to store a _S4Vectors::List_
of _GTuples_ objects. It extends the _GenomicRanges::GRangesList_ class.

Currently, all _GTuples_ in a _GTuplesList_ must have the
same `size`[^size]. I expect that users will mostly use _GTuples_ objects and 
have little need to directly use _GTuplesList_ objects.

[^size]: This may be changed in future versions of `r Biocpkg("GenomicTuples")`. 

```{r GTuplesList, eval = TRUE, echo = TRUE}
seqinfo <- Seqinfo(paste0("chr", 1:3), c(1000, 2000, 1500), NA, "mock1")
gt3 <- GTuples(seqnames = Rle(c("chr1", "chr2", "chr1", "chr3"),
                              c(1, 3, 2, 4)),
               tuples = matrix(c(1:10, 2:11, 3:12), ncol = 3),
               strand = Rle(strand(c("-", "+", "*", "+", "-")),
                            c(1, 2, 2, 3, 2)),
               score = 1:10, GC = seq(1, 0, length = 10), seqinfo = seqinfo)
gtl3 <- GTuplesList(A = gt3[1:5], B = gt3[6:10])
gtl3
```

For even more information on the _GTuplesList_ class, be sure to
consult the documentation:

```{r GTuplesList-help, eval = FALSE, echo = TRUE}
?GTuplesList
```

## _GTuplesList_ methods

Most methods defined for _GenomicRanges::GRangesList_ are also
applicable to _GTuplesList_. Those that are not yet defined,
which are those that make sense for ranges but generally not for tuples,
return error messages.

If a method that is not defined for _GTuplesList_ but is defined
for _GenomicRanges::GRangesList_ is truly required, then this can
be achieved by first coercing the _GTuplesList_ object to a
_GenomicRanges::GRangesList_ object, noting that this is
generally a destructive operation:

```{r GTuplesList-to-GRangesList, eval = TRUE, echo = TRUE}
as(gtl3, "GRangesList")
```

### Basic _GTuplesList_ accessors}

These are very similar to those available for _GTuples_ objects, except that 
they typically return a list since the input is now essentially a list of 
_GTuples_ objects:

```{r basic-gtupleslist-accessors1, eval = TRUE, echo = TRUE}
seqnames(gtl3)
# Returns a list of integer matrices
tuples(gtl3)
tuples(gtl3)[[1]]
strand(gtl3)
```

The `length` and `names` methods will return the length and
names of the list, respectively:

```{r basic-gtupleslist-accessors2, eval = TRUE, echo = TRUE}
length(gtl3)
names(gtl3)
```

_Seqinfo_ can be extracted using the `seqinfo` accessor:

```{r basic-gtupleslist-accessors3, eval = TRUE, echo = TRUE}
seqinfo(gtl3)
```

The `elementLengths` method returns a list of integers
corresponding to the result of calling `length` on each individual
_GTuples_ object contained by the _GTuplesList_. This is a
faster alternative to calling `lapply` on the _GTuplesList_:

```{r basic-gtupleslist-accessors4, eval = TRUE, echo = TRUE}
elementLengths(gtl3)
```

You can also use `isEmpty` to test if a _GTuplesList_ object 
contains anything:

```{r basic-gtupleslist-accessors5, eval = TRUE, echo = TRUE}
isEmpty(gtl3)
isEmpty(GTuplesList())
```

Finally, in the context of a _GTuplesList_ object, the
`mcols` method performs a similar operation to what it does on a
_GTuples_ object. However, this metadata now refers to
information at the list level instead of the level of the individual
_GTuples_ objects:

```{r basic-gtupleslist-accessors6, eval = TRUE, echo = TRUE}
mcols(gtl3) <- c("Feature A", "Feature B")
mcols(gtl3)
```

### Combining _GTuplesList_ objects

_GTuplesList_ objects can be unlisted to combine the separate
_GTuples_ objects that they contain as an expanded _GTuples_:

```{r combining-GTuplesLists, eval = TRUE, echo = TRUE}
ul <- unlist(gtl3)
ul
```

You can also combine _GTuplesList_ objects together using `append` or `c`.

### Subsetting _GTuplesList_ objects

Subsetting of _GTuplesList_ objects is identical to subsetting of
_GenomicRanges::GRangesList_ objects:

```{r GTuplesList-subsetting1, echo = TRUE, eval = TRUE}
gtl3[1]
gtl3[[1]]
gtl3["A"]
gtl3$B
```

When subsetting a _GTuplesList_, you can also pass in a second
parameter (as with a _GTuples_ object) to again specify which of
the metadata columns you wish to select:

```{r GTuplesList-subsetting2, echo = TRUE, eval = TRUE}
gtl3[1, "score"]
gtl3["B", "GC"]
```

The `head`, `tail`, `rep`, `rev`, and `window` methods all behave as you would 
expect them to for a _List_ object. For example, the elements referred to by 
`window` are now list elements instead of _GTuples_ elements:

```{r GTuplesList-subsetting3, echo = TRUE, eval = TRUE}
rep(gtl3[[1]], times = 3)
rev(gtl3)
head(gtl3, n = 1)
tail(gtl3, n = 1)
window(gtl3, start = 1, end = 1)
```

### Basic tuple operations for _GTuplesList_ objects

Basic tuple characteristics of _GTuplesList_ objects can be
extracted using the `start`, `end`, and `tuples`
methods. These are very similar to those available for _GTuples_
objects, except that they typically return a list since the input is now
essentially a list of _GTuples_ objects.

__WARNING: While the `width` method is well-defined, namely it returns an _IntegerList_ of $pos_{m} - pos_{1} + 1$, this is not generally what is desired or required. Instead, please see the `IPD` method that is discussed later.__

```{r GTuplesList-accessors, eval = TRUE, echo = TRUE}
start(gtl3)
end(gtl3)
tuples(gtl3)
```

#### Intra-tuple operations

Most of the intra-range methods defined for _GenomicRanges::GRangesList_ 
objects are not currently defined via extension for _GTuples_ objects due to 
the differences between ranges and tuples. Those not currently defined, and 
which return an error message, are:

- `flank`
- `promoters`
- `resize`
- `restrict`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

The `shift` method is well-defined:

```{r shift-GTuplesList, eval = TRUE, echo = TRUE}
shift(gtl3, 500)
shift(gtl3, IntegerList(A = 300L, B = 500L))
```

#### Inter-tuple operations

None of the inter-range methods defined for _GenomicRanges::GRangesList_ 
objects are currently defined via extension for _GTuplesList_ objects due to 
the differences between ranges and tuples. Those not currently defined, and 
which return an error message, are:

- `range`
- `reduce`
- `disjoin`
- `isDisjoint`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

#### Interval set operations for _GTuplesList_ objects

None of the interval set operations defined for
_GenomicRanges::GRangesList_ objects are currently defined via extension 
for _GTuplesList_ objects due to the differences between ranges and
tuples. Those not currently defined, and which return an error message,
are:

- `punion`
- `pintersect`
- `psetdiff`

I am happy to add these methods if appropriate, so please contact me if
you have suggestions for good definitions.

### Looping over _GTuplesList_ objects

Like for _GenomicRanges::GRangesList_ objects, for _GTuplesList_ objects there 
is a family of apply methods. These include `lapply`, `sapply`, `mapply`, 
`endoapply`, `mendoapply`, `Map`, and `Reduce`. The different looping methods 
defined for _GTuplesList_ objects are useful for returning different kinds of
results. The standard `lapply` and `sapply` behave according to convention, 
with the `lapply` method returning a list and `sapply` returning a more 
simplified output:

```{r GTuplesList-looping1, echo = TRUE, eval = TRUE}
lapply(gtl3, length)
sapply(gtl3, length)
```

As with _GenomicRanges::GRangesList_ objects, there is also a multivariate
version of `sapply`, called `mapply`, defined for _GTuplesList_ objects. And, 
if you don't want the results simplified, you can call the `Map` method, which 
does the same things as `mapply` but without simplifying the output:

```{r GTuplesList-looping2, echo = TRUE, eval = TRUE}
gtl3_shift <- shift(gtl3, 10)
names(gtl3) <- c("shiftA", "shiftB")
mapply(c, gtl3, gtl3_shift)
Map(c, gtl3, gtl3_shift)
```

The `endoapply` method will return the results as a _GTuplesList_ object rather 
than as a list:

```{r GTuplesList-looping3, echo = TRUE, eval = TRUE}
endoapply(gtl3, rev)
```

There is also a multivariate version of the `endoapply` method in the form of 
the `mendoapply` method:

```{r GTuplesList-looping4, echo = TRUE, eval = TRUE}
mendoapply(c, gtl3, gtl3_shift)
```

Finally, the `Reduce` method will allow the _GTuples_ objects to be collapsed 
across the whole of the _GTuplesList_ object:

```{r GTuplesList-looping5, echo = TRUE, eval = TRUE}
Reduce(c, gtl3)
```

### Additional methods unique to _GTuplesList_

Like _GTuples_, _GTuplesList_ have a few specifically defined methods that do 
not exist for _GenomicRanges::GRangesList_. These are `tuples`, `size` and 
`IPD`. These are identical to the methods for _GTuples_, except that they 
typically return a list since the input is now essentially a _List_ of _GTuples_ 
objects.

```{r unique-GTuplesList-methods, echo = TRUE, eval = TRUE}
tuples(gtl3)
tuples(gtl3)[[1]]
size(gtl3)
IPD(gtl3)
IPD(gtl3)[[1]]
```

## Implementation details

The _GTuplesList_ class extends the _GenomicRanges::GRangesList_ class.

# `findOverlaps`-based methods 

The definition of what constitutes an "overlap" between genomic tuples, or 
between genomic tuples and genomic ranges, lies at the heart of all 
`findOverlaps`-based methods[^findOverlaps] for _GTuples_ and _GTuplesList_
objects. 

[^findOverlaps]: The `findOverlaps`-based methods are `findOverlaps`, 
`countOverlaps`, `overlapsAny` and `subsetByOverlaps`.

I have chosen a definition that matches my intuition of what constitutes an "overlap" between genomic tuples or between genomic tuples and genomic 
ranges. However, I am open to suggestions on amending or extending this 
behaviour in future versions of `r Biocpkg("GenomicTuples")`.

## Definition of overlapping genomic tuples

I consider two genomic tuples to be _equal_ (`type = "equal"`) if they have 
identical sequence names (`seqnames`), strands (`strand`) and tuples 
(`tuples`). For 1-tuples and 2-tuples, this means we can simply
defer to the `findOverlaps`-based methods for
_GenomicRanges::GRanges_ and _GenomicRanges::GRangesList_
objects via inheritance. However, we cannot do the same for m-tuples
with $m > 2$ since this would ignore the "internal positions".
Therefore, I have implemented a special case of the
`findOverlaps` method for when `size` $> 2$ and
`type = "equal"`, which ensures that the "internal positions" are also checked 
for equality.

__In all other cases genomic tuples are treated as genomic ranges.__ This 
means that when `type = "any"`, `type = "start"`, `type = "end"` or 
`type = "within"` then the genomic tuples are treated as if they were genomic 
ranges. Specifically, _GTuples_ (resp. _GTuplesList_) are treated as though 
they were _GenomicRanges::GRanges_ (resp. _GenomicRanges::GRangesList_) with 
`pos1` = `start` and `posm` = `end`.

## Definition of overlapping genomic tuples and ranges

Genomic tuples are __always__ treated as genomic ranges when searching for overlaps between genomic tuples and genomic ranges.

## Examples

It is easiest to understand the above definitions by studying a few
examples.

Firstly, for 1-tuples where the _GTuples_ methods use the 
_GenomicRanges::GRanges_ methods:

```{r 1-tuples-findOverlaps-examples, eval = TRUE, echo = TRUE}
# Construct example 1-tuples
gt1 <- GTuples(seqnames = c('chr1', 'chr1', 'chr1', 'chr2'), 
               tuples = matrix(c(10L, 10L, 10L, 10L), ncol = 1), 
               strand = c('+', '-', '*', '+'))
# GRanges version of gt1
gr1 <- as(gt1, "GRanges")
findOverlaps(gt1, gt1, type = 'any')
# GTuples and GRanges methods identical
identical(findOverlaps(gt1, gt1, type = 'any'), 
          findOverlaps(gr1, gr1, type = 'any'))
findOverlaps(gt1, gt1, type = 'start')
# GTuples and GRanges methods identical
identical(findOverlaps(gt1, gt1, type = 'start'), 
          findOverlaps(gr1, gr1, type = 'start'))
findOverlaps(gt1, gt1, type = 'end')
# GTuples and GRanges methods identical
identical(findOverlaps(gt1, gt1, type = 'end'), 
          findOverlaps(gr1, gr1, type = 'end'))
findOverlaps(gt1, gt1, type = 'within')
# GTuples and GRanges methods identical
identical(findOverlaps(gt1, gt1, type = 'within'), 
          findOverlaps(gr1, gr1, type = 'within'))
findOverlaps(gt1, gt1, type = 'equal')
# GTuples and GRanges methods identical
identical(findOverlaps(gt1, gt1, type = 'equal'), 
          findOverlaps(gr1, gr1, type = 'equal'))
# Can pass other arguments, such as select and ignore.strand
findOverlaps(gt1, gt1, type = 'equal', ignore.strand = TRUE, select = 'last')
```

Next, for 2-tuples where the _GTuples_ methods use the
_GenomicRanges::GRanges_ methods:

```{r 2-tuples-findOverlaps-examples, eval = TRUE, echo = TRUE}
# Construct example 2-tuples
gt2 <- GTuples(seqnames = c('chr1', 'chr1', 'chr1', 'chr1', 'chr2'), 
               tuples = matrix(c(10L, 10L, 10L, 10L, 10L, 20L, 20L, 20L, 25L, 
                                 20L), ncol = 2), 
               strand = c('+', '-', '*', '+', '+'))
# GRanges version of gt2
gr2 <- as(gt2, "GRanges")
findOverlaps(gt2, gt2, type = 'any')
# GTuples and GRanges methods identical
identical(findOverlaps(gt2, gt2, type = 'any'), 
          findOverlaps(gr2, gr2, type = 'any'))
findOverlaps(gt2, gt2, type = 'start')
# GTuples and GRanges methods identical
identical(findOverlaps(gt2, gt2, type = 'start'), 
          findOverlaps(gr2, gr2, type = 'start'))
findOverlaps(gt2, gt2, type = 'end')
# GTuples and GRanges methods identical
identical(findOverlaps(gt2, gt2, type = 'end'), 
          findOverlaps(gr2, gr2, type = 'end'))
findOverlaps(gt2, gt2, type = 'within')
# GTuples and GRanges methods identical
identical(findOverlaps(gt2, gt2, type = 'within'), 
          findOverlaps(gr2, gr2, type = 'within'))
findOverlaps(gt2, gt2, type = 'equal')
# GTuples and GRanges methods identical
identical(findOverlaps(gt2, gt2, type = 'equal'), 
          findOverlaps(gr2, gr2, type = 'equal'))
# Can pass other arguments, such as select and ignore.strand
findOverlaps(gt2, gt2, type = 'equal', ignore.strand = TRUE, select = 'last')
```

Finally, for m-tuples with $m > 2$ where _GTuples_ methods use the
_GenomicRanges::GRanges_ methods __unless `type = "equal"`__:

```{r 3-tuples-findOverlaps-examples, eval = TRUE, echo = TRUE}
# Construct example 3-tuples
gt3 <- GTuples(seqnames = c('chr1', 'chr1', 'chr1', 'chr1', 'chr2'), 
               tuples = matrix(c(10L, 10L, 10L, 10L, 10L, 20L, 20L, 20L, 25L, 
                                 20L, 30L, 30L, 35L, 30L, 30L), ncol = 3), 
               strand = c('+', '-', '*', '+', '+'))
# GRanges version of gt3
gr3 <- as(gt3, "GRanges")
findOverlaps(gt3, gt3, type = 'any')
# GTuples and GRanges methods identical
identical(findOverlaps(gt3, gt3, type = 'any'), 
          findOverlaps(gr3, gr3, type = 'any')) # TRUE

findOverlaps(gt3, gt3, type = 'start')
# GTuples and GRanges methods identical
identical(findOverlaps(gt3, gt3, type = 'start'), 
          findOverlaps(gr3, gr3, type = 'start')) # TRUE

findOverlaps(gt3, gt3, type = 'end')
# GTuples and GRanges methods identical
identical(findOverlaps(gt3, gt3, type = 'end'), 
          findOverlaps(gr3, gr3, type = 'end')) # TRUE

findOverlaps(gt3, gt3, type = 'within')
# GTuples and GRanges methods identical
identical(findOverlaps(gt3, gt3, type = 'within'), 
          findOverlaps(gr3, gr3, type = 'within')) # TRUE

findOverlaps(gt3, gt3, type = 'equal')
# GTuples and GRanges methods **not** identical because  GRanges method ignores 
# "internal positions".
identical(findOverlaps(gt3, gt3, type = 'equal'), 
          findOverlaps(gr3, gr3, type = 'equal')) # FALSE
# Can pass other arguments, such as select and ignore.strand
findOverlaps(gt3, gt3, type = 'equal', ignore.strand = TRUE, select = 'last')
```

# Comparison of genomic tuples

I have chosen a definition that matches my intuition of what constitutes a  
comparison between genomic tuples. However, I am open to suggestions 
on amending or extending this behaviour in future versions of 
`r Biocpkg("GenomicTuples")`.

## Definition of comparison methods for genomic tuples

The comparison of two genomic tuples, `x` and `y`, is done by 
first comparing the `seqnames(x)` to `seqnames(y)`, then 
`strand(x)` to `strand(y)` and finally `tuples(x)` to `tuples(y)`. 

Ordering of `seqnames` and `strand` is as implemented _GenomicRanges::GRanges_. 
Ordering of `tuples` is element-wise, i.e. $pos_{1}, \ldots, pos_{m}$ are 
compared in turn. For example, `chr1:+:10, 20, 30` is considered less than 
`chr1:+:10, 20, 40`. This defines what I will refer to as the "natural order" 
of genomic tuples.

The above is implemented in the `compare` method for 
_GTuples_, which performs "generalized range-wise comparison" of two 
_GTuples_ objects, `x` and `y`. That is, `compare(x, y)` returns an integer 
vector where the $i^{th}$ element is a code describing how the $i^{th}$ element 
in `x` is qualitatively positioned relatively to the $i^{th}$ element in `y`. 
A code that is `< 0`, `= 0`, or `> 0`, corresponds to `x[i] < y[i]`, 
`x[i] == y[i]`, or `x[i] > y[i]`, respectively.

The 6 traditional binary comparison operators (`==`, `!=`, `<=`, `>=`, `<`, and 
`>`), other comparison operators (`match`, `order`, `sort`, and `rank`) and 
duplicate-based methods (`duplicated` and `unique`) all use this "natural 
order".

## Examples

It is easiest to understand the above definitions by studying a few
examples, here using 3-tuples:

```{r 3-tuples-compare-examples, eval = TRUE, echo = TRUE}
# Construct example 3-tuples
gt3 <- GTuples(seqnames = c('chr1', 'chr1', 'chr1', 'chr1', 'chr2', 'chr1', 
                            'chr1'), 
               tuples = matrix(c(10L, 10L, 10L, 10L, 10L, 5L, 10L, 20L, 20L, 
                                 20L, 25L, 20L, 20L, 20L, 30L, 30L, 35L, 30L, 
                                 30L, 30L, 35L), 
                               ncol = 3), 
               strand = c('+', '-', '*', '+', '+', '+', '+'))
gt3

# Compare each tuple to itself
compare(gt3, gt3)
gt3 < gt3
gt3 > gt3
gt3 == gt3

# Compare the third tuple to all tuples
compare(gt3[3], gt3)
gt3[3] < gt3
gt3[3] > gt3
gt3[3] == gt3

## Some comparisons where tuples differ only in one coordinate

# Ordering of seqnames 
# 'chr1' < 'chr2' for tuples with otherwise identical coordinates
gt3[1] < gt3[5] # TRUE

# Ordering of strands
# '+' < '-' < '*' for tuples with otherwise identical coordiantes
gt3[1] < gt3[2] # TRUE
gt3[1] < gt3[2] # TRUE
gt3[1] < unstrand(gt3[2]) # TRUE
gt3[2] < unstrand(gt3[2]) # TRUE

# Ordering of tuples
# Tuples checked sequentially from pos1, ..., posm for tuples with otherwise
# identical coordinates
gt3[6] < gt3[1] # TRUE due to pos1
gt3[2] < gt3[4] # TRUE due to pos2
gt3[1] < gt3[7] # TRUE due to pos3

# Sorting of tuples
# Sorted first by seqnames, then by strand, then by tuples
sort(gt3)

# Duplicate tuples
# Duplicate tuples must have identical seqnames, strand and positions (tuples)
duplicated(c(gt3, gt3[1:3]))
unique(c(gt3, gt3[1:3]))
```

# Acknowledgements

I am very grateful to all the Bioconductor developers but particularly wish 
to thank the developers of `r Biocpkg("GenomicRanges")` ([Lawrence, M. et al. Software for computing and annotating genomic ranges. PLoS Comput. Biol. 9, e1003118 (2013).](http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1003118)), which 
`r Biocpkg("GenomicTuples")` uses heavily and is based upon. A special thanks to Hervé Pagès for his assistance and fixes when making upstream changes to `r Biocpkg("GenomicRanges")`.

# Session info

Here is the output of `sessionInfo` on the system on which
this document was compiled:

```{r sessionInfo, eval = TRUE, echo = TRUE}
sessionInfo()
```

# References

- [Lawrence, M. et al. Software for computing and annotating genomic ranges. PLoS Comput. Biol. 9, e1003118 (2013).](http://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1003118)

