snpgdsPCA {SNPRelate} | R Documentation

## Principal Component Analysis (PCA) on SNP genotype data

### Description

To calculate the eigenvectors and eigenvalues for principal component analysis in GWAS.

### Usage

    snpgdsPCA(gdsobj, sample.id=NULL, snp.id=NULL,
        autosome.only=TRUE, remove.monosnp=TRUE, maf=NaN, missing.rate=NaN,
        algorithm=c("exact", "randomized"),
        eigen.cnt=ifelse(identical(algorithm, "randomized"), 16L, 32L),
        num.thread=1L, bayesian=FALSE, need.genmat=FALSE,
        genmat.only=FALSE, eigen.method=c("DSPEVX", "DSPEV"),
        aux.dim=eigen.cnt*2L, iter.num=10L, verbose=TRUE)
    ## S3 method for class 'snpgdsPCAClass'
    plot(x, eig=c(1L,2L), ...)

### Arguments

`gdsobj` | an object of class `SNPGDSFileClass`, a SNP GDS file
`sample.id` | a vector of sample id specifying selected samples; if NULL, all samples are used
`snp.id` | a vector of snp id specifying selected SNPs; if NULL, all SNPs are used
`autosome.only` | if `TRUE`, use autosomal SNPs only; if it is a numeric or character value, keep SNPs according to the specified chromosome
`remove.monosnp` | if TRUE, remove monomorphic SNPs
`maf` | to use the SNPs with ">= maf" only; if NaN, no MAF threshold
`missing.rate` | to use the SNPs with "<= missing.rate" only; if NaN, no missing threshold
`eigen.cnt` | output the number of eigenvectors; if eigen.cnt <= 0, then return all eigenvectors
`algorithm` | "exact", traditional exact calculation; "randomized", fast PCA with randomized algorithm introduced in Galinsky et al. 2016
`num.thread` | the number of (CPU) cores used; if `NA`, detect the number of cores automatically
`bayesian` | if TRUE, use bayesian normalization
`need.genmat` | if TRUE, return the genetic covariance matrix
`genmat.only` | return the genetic covariance matrix only, do not compute the eigenvalues and eigenvectors
`eigen.method` | "DSPEVX" – compute the top `eigen.cnt` eigenvalues and eigenvectors using LAPACK::DSPEVX; "DSPEV" – to be compatible with SNPRelate_1.1.6 or earlier, using LAPACK::DSPEV; "DSPEVX" is significantly faster than "DSPEV" if only top principal components are of interest
`aux.dim` | auxiliary dimension used in fast randomized algorithm
`iter.num` | iteration number used in fast randomized algorithm
`verbose` | if TRUE, show information
`x` | a `snpgdsPCAClass` object
`eig` | indices of eigenvectors, like `1:2` or `1:4`
`...` | the arguments passed to or from other methods, like `pch`, `col`

### Details

The minor allele frequency and missing rate for each SNP passed in `snp.id` are calculated over all the samples in `sample.id`.

### Value

Return a `snpgdsPCAClass` object, and it is a list:

`sample.id` | the sample ids used in the analysis
`snp.id` | the SNP ids used in the analysis
`eigenval` | eigenvalues
`eigenvect` | eigenvactors, "# of samples" x "eigen.cnt"
`varprop` | variance proportion for each principal component
`TraceXTX` | the trace of the genetic covariance matrix
`Bayesian` | whether use bayerisan normalization
`genmat` | the genetic covariance matrix

### Author(s)

Xiuwen Zheng

### References

Patterson N, Price AL, Reich D. Population structure and eigenanalysis. PLoS Genet. 2006 Dec;2(12):e190.

Galinsky KJ, Bhatia G, Loh PR, Georgiev S, Mukherjee S, Patterson NJ, Price AL. Fast Principal-Component Analysis Reveals Convergent Evolution of ADH1B in Europe and East Asia. Am J Hum Genet. 2016 Mar 3;98(3):456-72. doi: 10.1016/j.ajhg.2015.12.022. Epub 2016 Feb 25.

### See Also

`snpgdsPCACorr`, `snpgdsPCASNPLoading`, `snpgdsPCASampLoading`, `snpgdsAdmixProp`, `snpgdsEIGMIX`

### Examples

    # open an example dataset (HapMap)
    genofile <- snpgdsOpen(snpgdsExampleFileName())

    # run PCA
    RV <- snpgdsPCA(genofile)

    # eigenvalues
    head(RV$eigenval)

    # variance proportion (%)
    head(round(RV$varprop*100, 2))
    # [1] 12.23  5.84  1.01  0.95  0.84  0.74

    plot(RV)
    plot(RV, 1:4)

    ####  there is no population information  ####

    # make a data.frame
    tab <- data.frame(sample.id = RV$sample.id,
        EV1 = RV$eigenvect[,1],    # the first eigenvector
        EV2 = RV$eigenvect[,2],    # the second eigenvector
        stringsAsFactors = FALSE)
    head(tab)
    #   sample.id         EV1         EV2
    # 1   NA19152 -0.08411287 -0.01226860
    # 2   NA19139 -0.08360644 -0.01085849
    # 3   NA18912 -0.08110808 -0.01184524
    # 4   NA19160 -0.08680864 -0.01447106
    # 5   NA07034  0.03109761  0.07709255
    # 6   NA07055  0.03228450  0.08155730

    # draw
    plot(tab$EV2, tab$EV1, xlab="eigenvector 2", ylab="eigenvector 1")

    ####  there are population information  ####

    # get population information
    #   or pop_code <- scan("pop.txt", what=character())
    #   if it is stored in a text file "pop.txt"
    pop_code <- read.gdsn(index.gdsn(genofile, "sample.annot/pop.group"))

    # get sample id
    samp.id <- read.gdsn(index.gdsn(genofile, "sample.id"))

    # assume the order of sample IDs is as the same as population codes
    cbind(samp.id, pop_code)
    #        samp.id       pop_code
    #   [1,] "NA19152"     "YRI"
    #   [2,] "NA19139"     "YRI"
    #   [3,] "NA18912"     "YRI"
    #   [4,] "NA19160"     "YRI"
    #   [5,] "NA07034"     "CEU"
    #   ...

    # make a data.frame
    tab <- data.frame(sample.id = RV$sample.id,
        pop = factor(pop_code)[match(RV$sample.id, samp.id)],
        EV1 = RV$eigenvect[,1],    # the first eigenvector
        EV2 = RV$eigenvect[,2],    # the second eigenvector
        stringsAsFactors = FALSE)
    head(tab)
    #   sample.id pop         EV1         EV2
    # 1   NA19152 YRI -0.08411287 -0.01226860
    # 2   NA19139 YRI -0.08360644 -0.01085849
    # 3   NA18912 YRI -0.08110808 -0.01184524
    # 4   NA19160 YRI -0.08680864 -0.01447106
    # 5   NA07034 CEU  0.03109761  0.07709255
    # 6   NA07055 CEU  0.03228450  0.08155730

    # draw
    plot(tab$EV2, tab$EV1, col=as.integer(tab$pop),
        xlab="eigenvector 2", ylab="eigenvector 1")
    legend("bottomright", legend=levels(tab$pop), pch="o", col=1:4)

    # close the file
    snpgdsClose(genofile)

[Package SNPRelate version 1.14.0 Index]