snpgdsPCASNPLoading {SNPRelate} | R Documentation

## SNP loadings in principal component analysis

### Description

To calculate the SNP loadings in Principal Component Analysis

### Usage

    snpgdsPCASNPLoading(pcaobj, gdsobj, num.thread=1L, verbose=TRUE)

### Arguments

`pcaobj` | a `snpgdsPCAClass` object returned from the function snpgdsPCA or a `snpgdsEigMixClass` from snpgdsEIGMIX
`gdsobj` | an object of class `SNPGDSFileClass`, a SNP GDS file
`num.thread` | the number of (CPU) cores used; if `NA`, detect the number of cores automatically
`verbose` | if TRUE, show information

### Details

Calculate the SNP loadings (or SNP eigenvectors) from the principal component analysis conducted in `snpgdsPCA`.

### Value

Returns a `snpgdsPCASNPLoading` object if `pcaobj` is `snpgdsPCAClass`, which is a list:

`sample.id` | the sample ids used in the analysis
`snp.id` | the SNP ids used in the analysis
`eigenval` | eigenvalues
`snploading` | SNP loadings, or SNP eigenvectors
`TraceXTX` | the trace of the genetic covariance matrix
`Bayesian` | whether use bayerisan normalization
`avgfreq` | two times allele frequency used in `snpgdsPCA`
`scale` | internal parameter

Or returns a `snpgdsEigMixSNPLoadingClass` object if `pcaobj` is `snpgdsEigMixClass`, which is a list:

`sample.id` | the sample ids used in the analysis
`snp.id` | the SNP ids used in the analysis
`eigenval` | eigenvalues
`snploading` | SNP loadings, or SNP eigenvectors
`afreq` | allele frequency

### Author(s)

Xiuwen Zheng

### References

Patterson N, Price AL, Reich D (2006) Population structure and eigenanalysis. PLoS Genetics 2:e190.

Price AL, Patterson NJ, Plenge RM, Weinblatt ME, Shadick NA, Reich D (2006) Principal components analysis corrects for stratification in genome-wide association studies. Nat Genet. 38, 904-909.

Zhu, X., Li, S., Cooper, R. S., and Elston, R. C. (2008). A unified association analysis approach for family and unrelated samples correcting for stratification. Am J Hum Genet, 82(2), 352-365.

### See Also

`snpgdsPCA`, `snpgdsEIGMIX`, `snpgdsPCASampLoading`, `snpgdsPCACorr`

### Examples

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

    PCARV <- snpgdsPCA(genofile, eigen.cnt=8)
    SnpLoad <- snpgdsPCASNPLoading(PCARV, genofile)

    names(SnpLoad)
    # [1] "sample.id"  "snp.id"     "eigenval"   "snploading" "TraceXTX"
    # [6] "Bayesian"   "avgfreq"    "scale"
    dim(SnpLoad$snploading)
    # [1]     8 8722

    plot(SnpLoad$snploading[1,], type="h", ylab="PC 1")

    # close the genotype file
    snpgdsClose(genofile)

[Package SNPRelate version 1.20.1 Index]