hg18 {rCGH} | R Documentation

## Hg18 Chromosome Lengths and Centromere Locations

### Description

A data set containing lengths and centromere locations for each of the 24 chromosomes, according to Hg18.

### Usage

    hg18

### Format

A data set with 24 rows and 5 columns:

- chrom: chromosome number.

- length: chromosome length.

- centromerStart: centromere start position.

- centromerEnd: centromere start position.

- cumlen: cumulative length (where the previous chromosome ends).

### Value

a data set.

### Author(s)

Frederic Commo

### Source

These data derived from the Hg18 gap UCSC table, freely available at: UCSC
Access date: 10-10-2015
Within the browser, select:
group: All Tables
database: hg18
table: gap

### Examples

    # For users convenience, we provide a prebuilt dataset
    # containing the Hg18 chr lengths, and centromeres location.
    hg18

    # The same dataset can be obtained as follow:
    ## Not run:
    library(BSgenome)
    library(rtracklayer)

    getChrLength <- function(genome){
        genome <- sprintf("BSgenome.Hsapiens.UCSC.
        g <- getBSgenome(genome, masked=FALSE)
        data.frame(chrom=1:24, length=seqlengths(g)[1:24])
    }
    .chrAsNum <- function(tbl){
        tbl$chrom <- gsub("chr", "", tbl$chrom)
        tbl$chrom[tbl$chrom=="X"] <- 23
        tbl$chrom[tbl$chrom=="Y"] <- 24
        tbl$chrom <- as.numeric(tbl$chrom)
        tbl[order(tbl$chrom),]
    }
    getCentromeres <- function(genome){
        mySession <- try(browserSession("UCSC"), silent=TRUE)
        # In case it fails, use another mirror
        if(inherits(mySession, "try-error"))
            mySession <- browserSession("UCSC",
                                        url="http://genome-euro.ucsc.edu/cgi-bin/")
        genome(mySession) <- genome
        obj <- ucscTableQuery(mySession, table="gap")
        tbl <- getTable(obj)
        tbl <- tbl[tbl$type=="centromere", c("chrom", "chromStart", "chromEnd")]
        colnames(tbl)[2:3] <- c("centromerStart", "centromerEnd")
        .chrAsNum(tbl)
    }
    makeHg <- function(genome){
        chrL <- getChrLength(genome)
        ctm <- getCentromeres(genome)
        tbl <- merge(chrL, ctm, by="chrom")
        cumlen <- c(0, cumsum(as.numeric(tbl$length))[-nrow(tbl)])
        cbind.data.frame(tbl, cumlen=cumlen)
    }
    hg18 <- makeHg("hg18")
    hg18

    ## End(Not run)

[Package rCGH version 1.20.0 Index]