bed.loadings | R Documentation |
Compute the loadings corresponding to given PCs.
bed.loadings(x, pc)
x |
A |
pc |
A matrix with Principal Components in columns |
A matrix with the corresponding loadings in columns.
Hervé Perdry and Claire Dandine-Roulland
# load chr2 data set (~10k SNPs in low LD) x <- read.bed.matrix( system.file("extdata", "chr2.bed", package="gaston") ) # Compute Genetic Relationship Matrix standardize(x) <- "p" K <- GRM(x) # Eigen decomposition eiK <- eigen(K) # deal with small negative eigen values eiK$values[ eiK$values < 0 ] <- 0 # Note: the eigenvectors are normalized, to compute 'true' PCs # multiply them by the square root of the associated eigenvalues PC <- sweep(eiK$vectors, 2, sqrt(eiK$values), "*") # Compute loadings for the 2 first PCs # one can use PC[,1:2] instead of eiK$vectors[,1:2] as well L <- bed.loadings(x, eiK$vectors[,1:2]) dim(L) head(L) # the loadings are normalized colSums(L**2) # Verify that these are loadings head( (x %*% L) / sqrt(ncol(x)-1) ) head( PC[,1:2] )
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