hlaAttrBagging {HIBAG} | R Documentation

## Build a HIBAG model

### Description

To build a HIBAG model for predicting HLA types with SNP markers.

### Usage

    hlaAttrBagging(hla, snp, nclassifier=100L, mtry=c("sqrt", "all", "one"),
        prune=TRUE, na.rm=TRUE, verbose=TRUE, verbose.detail=FALSE)

### Arguments

`hla` | the training HLA types, an object of `hlaAlleleClass`
`snp` | the training SNP genotypes, an object of `hlaSNPGenoClass`
`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
`verbose` | if TRUE, show information
`verbose.detail` | if TRUE, show more information

### Details

`mtry` (the number of variables randomly sampled as candidates for each selection, "sqrt" by default): `"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 on non-informative SNP markers.

A parallel version of `hlaAttrBagging` is `hlaParallelAttrBagging`.

### Value

Return an object of `hlaAttrBagClass`:

`n.samp` | the total number of training samples
`n.snp` | the total number of candidate SNP predictors
`sample.id` | the sample IDs
`snp.id` | the SNP IDs
`snp.position` | SNP position in basepair
`snp.allele` | a vector of characters with the format of “A allele/B allele”
`snp.allele.freq` | the allele frequencies
`hla.locus` | the name of HLA locus
`hla.allele` | the HLA alleles used in the model
`hla.freq` | the HLA allele frequencies
`assembly` | the human genome reference, such like "hg19"
`model` | internal use
`matching` | matching proportion in the training set

### 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

`hlaClose`, `hlaParallelAttrBagging`, `summary.hlaAttrBagClass`, `predict.hlaAttrBagClass`, `hlaPredict`

### 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))

    # train a HIBAG model
    set.seed(100)
    # please use "nclassifier=100" when you use HIBAG for real data
    model <- hlaAttrBagging(hlatab$training, train.geno, nclassifier=4,
        verbose.detail=TRUE)
    summary(model)

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

    # compare
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0))
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0.5))

    # save the parameter file
    mobj <- hlaModelToObj(model)
    save(mobj, file="HIBAG_model.RData")
    save(test.geno, file="testgeno.RData")
    save(hlatab, file="HLASplit.RData")

    # Clear Workspace
    hlaClose(model)  # release all resources of model
    rm(list = ls())

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

    # NOW, load a HIBAG model from the parameter file
    mobj <- get(load("HIBAG_model.RData"))
    model <- hlaModelFromObj(mobj)

    # validation
    test.geno <- get(load("testgeno.RData"))
    hlatab <- get(load("HLASplit.RData"))

    pred <- predict(model, test.geno, type="response")
    summary(pred)

    # compare
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0))
    (comp <- hlaCompareAllele(hlatab$validation, pred, allele.limit=model,
        call.threshold=0.5))

    # delete the temporary files
    unlink(c("HIBAG_model.RData", "testgeno.RData", "HLASplit.RData"), force=TRUE)

[Package HIBAG version 1.18.1 Index]