hlaParallelAttrBagging {HIBAG} | R Documentation

## Build a HIBAG model via parallel computation

### Description

To build a HIBAG model for predicting HLA types via parallel computation.

### Usage

    hlaParallelAttrBagging(cl, hla, snp, auto.save="",
        nclassifier=100L, mtry=c("sqrt", "all", "one"), prune=TRUE, na.rm=TRUE,
        stop.cluster=FALSE, verbose=TRUE)

### Arguments

`cl` | if a cluster object, created by the package parallel-package; if `NULL`, serial implementation will be performed; if numeric, specify the number of cores
`hla` | training HLA types, an object of `hlaAlleleClass`
`snp` | training SNP genotypes, an object of `hlaSNPGenoClass`
`auto.save` | specify a autosaved file, see details
`nclassifier` | the total number of individual classifiers
`mtry` | a character or a numeric value, the number of variables randomly sampled as candidates for each selection. See details
`prune` | if TRUE, to perform a parsimonious forward variable selection, otherwise, exhaustive forward variable selection. See details
`na.rm` | if TRUE, remove the samples with missing HLA types
`stop.cluster` | `TRUE`: stop cluster nodes after computing
`verbose` | if TRUE, show information

### Details

`mtry` (the number of variables randomly sampled as candidates for each selection): `"sqrt"`, using the square root of the total number of candidate SNPs; `"all"`, using all candidate SNPs; `"one"`, using one SNP; `an integer`, specifying the number of candidate SNPs; `0 < r < 1`, the number of candidate SNPs is "r * the total number of SNPs".

`prune`: there is no significant difference on accuracy between parsimonious and exhaustive forward variable selections. If `prune = TRUE`, the searching algorithm performs a parsimonious forward variable selection: if a new SNP predictor reduces the current out-of-bag accuracy, then it is removed from the candidate SNP set for future searching. Parsimonious selection helps to improve the computational efficiency by reducing the searching times of non-informative SNP markers.

### Value

Return an object of `hlaAttrBagClass` if `auto.save=""`.

### Author(s)

Xiuwen Zheng

### References

Zheng X, Shen J, Cox C, Wakefield J, Ehm M, Nelson M, Weir BS; HIBAG – HLA Genotype Imputation with Attribute Bagging. Pharmacogenomics Journal. doi: 10.1038/tpj.2013.18. http://www.nature.com/tpj/journal/v14/n2/full/tpj201318a.html

### See Also

`hlaAttrBagging`, `hlaClose`

### Examples

    # make a "hlaAlleleClass" object
    hla.id <- "A"
    hla <- hlaAllele(HLA_Type_Table$sample.id,
        H1 = HLA_Type_Table[, paste(hla.id, ".1", sep="")],
        H2 = HLA_Type_Table[, paste(hla.id, ".2", sep="")],
        locus=hla.id, assembly="hg19")

    # divide HLA types randomly
    set.seed(100)
    hlatab <- hlaSplitAllele(hla, train.prop=0.5)
    names(hlatab)
    # "training"   "validation"
    summary(hlatab$training)
    summary(hlatab$validation)

    # SNP predictors within the flanking region on each side
    region <- 500   # kb
    snpid <- hlaFlankingSNP(HapMap_CEU_Geno$snp.id, HapMap_CEU_Geno$snp.position,
        hla.id, region*1000, assembly="hg19")
    length(snpid)  # 275

    # training and validation genotypes
    train.geno <- hlaGenoSubset(HapMap_CEU_Geno,
        snp.sel = match(snpid, HapMap_CEU_Geno$snp.id),
        samp.sel = match(hlatab$training$value$sample.id,
        HapMap_CEU_Geno$sample.id))
    test.geno <- hlaGenoSubset(HapMap_CEU_Geno,
        samp.sel=match(hlatab$validation$value$sample.id,
        HapMap_CEU_Geno$sample.id))

    #############################################################################

    set.seed(100)

    # train a HIBAG model in parallel with 2 cores
    # please use "nclassifier=100" when you use HIBAG for real data
    model <- hlaParallelAttrBagging(2, hlatab$training, train.geno, nclassifier=4)

    #############################################################################

    library(parallel)

    # use option cl.core to choose an appropriate cluster size.
    cl <- makeCluster(getOption("cl.cores", 2))
    set.seed(100)

    # train a HIBAG model in parallel
    # please use "nclassifier=100" when you use HIBAG for real data
    hlaParallelAttrBagging(cl, hlatab$training, train.geno, nclassifier=4,
        auto.save="tmp_model.RData", stop.cluster=TRUE)

    mobj <- get(load("tmp_model.RData"))
    summary(mobj)
    model <- hlaModelFromObj(mobj)

    # validation
    pred <- predict(model, test.geno)
    summary(pred)

    # compare
    hlaCompareAllele(hlatab$validation, pred, allele.limit=model)$overall

    # since 'stop.cluster=TRUE' used in 'hlaParallelAttrBagging'
    # need a new cluster
    cl <- makeCluster(getOption("cl.cores", 2))

    pred <- predict(model, test.geno, cl=cl)
    summary(pred)

    # stop parallel nodes
    stopCluster(cl)

    # delete the temporary file
    unlink(c("tmp_model.RData"), force=TRUE)

[Package HIBAG version 1.18.1 Index]