seqCluster {clusterExperiment} | R Documentation

## Program for sequentially clustering, removing cluster, and starting again.

### Description

Given a data matrix, this function will call clustering routines, and sequentially remove best clusters, and iterate to find clusters.

### Usage

    seqCluster(x = NULL, diss = NULL, k0, subsample = TRUE, beta,
      top.can = 5, remain.n = 30, k.min = 3, k.max = k0 + 10,
      verbose = TRUE, subsampleArgs = NULL, mainClusterArgs = NULL,
      checkDiss = FALSE)

### Arguments

`x` | `p x n` data matrix on which to run the clustering (samples in columns).
`diss` | `n x n` data matrix of dissimilarities between the samples on which to run the clustering
`k0` | the value of K at the first iteration of sequential algorithm, see details below or vignette.
`subsample` | logical as to whether to subsample via `subsampleClustering` to get the distance matrix at each iteration; otherwise the distance matrix is set by arguments to `mainClustering`.
`beta` | value between 0 and 1 to decide how stable clustership membership has to be before 'finding' and removing the cluster.
`top.can` | only the top.can clusters from `mainClustering` (ranked by 'orderBy' argument given to `mainClustering`) will be compared pairwise for stability. Making this very big will effectively remove this parameter and all pairwise comparisons of all clusters found will be considered. This might result in smaller clusters being found. The current default is fairly large, so probably will have little effect.
`remain.n` | when only this number of samples are left (i.e. not yet clustered) then algorithm will stop.
`k.min` | each iteration of sequential detection of clustering will decrease the beginning K of subsampling, but not lower than k.min.
`k.max` | algorithm will stop if K in iteration is increased beyond this point.
`verbose` | whether the algorithm should print out information as to its progress.
`subsampleArgs` | list of arguments to be passed to `subsampleClustering`.
`mainClusterArgs` | list of arguments to be passed to `mainClustering`).
`checkDiss` | logical. Whether to check whether the input `diss` is valid.

### Details

`seqCluster` is not meant to be called by the user. It is only an exported function so as to be able to clearly document the arguments for `seqCluster` which can be passed via the argument `seqArgs` in functions like `clusterSingle` and `clusterMany`.

This code is adapted from the sequential protion of the code of the tightClust package of Tseng and Wong. At each iteration of the algorithm it finds a set of samples that constitute a homogeneous cluster and remove them, and iterate again to find the next set of samples that form a cluster.

In each iteration, to determine the next set of homogeneous set of samples, the algorithm will iteratively cluster the current set of samples for a series of increasing values of the parameter $K$, starting at a value `kinit` and increasing by 1 at each iteration, until a sufficiently homogeneous set of clusters is found. For the first set of homogeneous samples, `kinit` is set to the argument $k0$, and for iteration, `kinit` is increased internally.

Depending on the value of `subsample` how the value of $K$ is used differs. If `subsample=TRUE`, $K$ is the `k` sent to the cluster function `clusterFunction` sent to `subsampleClustering` via `subsampleArgs`; then `mainClustering` is run on the result of the co-occurance matrix from `subsampleClustering` with the `ClusterFunction` object defined in the argument `clusterFunction` set via `mainClusterArgs`. The number of clusters actually resulting from this run of `mainClustering` may not be equal to the $K$ sent to the clustering done in `subsampleClustering`. If `subsample=FALSE`, `mainClustering` is called directly on the data to determine the clusters and $K$ set by `seqCluster` for this iteration determines the parameter of the clustering done by `mainClustering`. Specifically, the argument `clusterFunction` defines the clustering of the `mainClustering` step and `k` is sent to that `ClusterFunction` object. This means that if `subsample=FALSE`, the `clusterFunction` must be of `algorithmType` "K".

In either setting of `subsample`, the resulting clusters from `mainClustering` for a particular $K$ will be compared to clusters found in the previous iteration of $K-1$. For computational (and other?) convenience, only the first `top.can` clusters of each iteration will be compared to the first `top.can` clusters of previous iteration for similarity (where `top.can` currently refers to ordering by size, so first `top.can` largest clusters.

If there is no cluster of the first `top.can` in the current iteration $K$ that has overlap similarity > `beta` to any in the previous iteration, then the algorithm will move to the next iteration, increasing to $K+1$.

If, however, of these clusters there is a cluster in the current iteration $K$ that has overlap similarity > beta to a cluster in the previous iteration $K-1$, then the cluster with the largest such similarity will be identified as a homogenous set of samples and the samples in it will be removed and designated as such. The algorithm will then start again to determine the next set of homogenous samples, but without these samples. Furthermore, in this case (i.e. a cluster was found and removed), the value of `kinit` will be be reset to `kinit-1`; i.e. the range of increasing $K$ that will be iterated over to find a set of homogenous samples will start off one value less than was the case for the previous set of homogeneous samples. If `kinit-1`<`k.min`, then `kinit` will be set to `k.min`.

If there are less than `remain.n` samples left after finding a cluster and removing its samples, the algorithm will stop, as subsampling is deamed to no longer be appropriate. If the K has to be increased to beyond `k.max` without finding any pair of clusters with overlap > beta, then the algorithm will stop. Any samples not found as part of a homogenous set of clusters at that point will be classified as unclustered (given a value of -1)

Certain combinations of inputs to `mainClusterArgs` and `subsampleArgs` are not allowed. See `clusterSingle` for these explanations.

### Value

A list with values

- `clustering` a vector of length equal to nrows(x) giving the integer-valued cluster ids for each sample. The integer values are assigned in the order that the clusters were found. "-1" indicates the sample was not clustered.

- `clusterInfo` if clusters were successfully found, a matrix of information regarding the algorithm behavior for each cluster (the starting and stopping K for each cluster, and the number of iterations for each cluster).

- `whyStop` a character string explaining what triggered the algorithm to stop.

### References

Tseng and Wong (2005), "Tight Clustering: A Resampling-Based Approach for Identifying Stable and Tight Patterns in Data", Biometrics, 61:10-16.

### See Also

tight.clust, `clusterSingle`,`mainClustering`,`subsampleClustering`

### Examples

    ## Not run:
    data(simData)

    set.seed(12908)
    clustSeqHier <- seqCluster(simData, k0=5, subsample=TRUE,
    beta=0.8, subsampleArgs=list(resamp.n=100,
    samp.p=0.7, clusterFunction="kmeans", clusterArgs=list(nstart=10)),
    mainClusterArgs=list(minSize=5,clusterFunction="hierarchical01",clusterArgs=list(alpha=0.1)))

    ## End(Not run)

[Package clusterExperiment version 2.7.2 Index]