Question: PCA from deseq and r function differ
gravatar for tonja.r
18 months ago by
United Kingdom
tonja.r10 wrote:

I stabilize my data with rlog and then plot PCA with the DESeq proposed method. 

dds = DESeqDataSetFromMatrix(countData=histone_m, colData=Design, design=~condition)
met = rlog(dds)     
data <- plotPCA(met, intgroup=c("condition"), returnData=TRUE)
percentVar <- round(100 * attr(data, "percentVar"))
myPlot = ggplot(data, aes(PC1, PC2, color=name)) +
       geom_point(size=3) +
        xlab(paste0("PC1: ",percentVar[1],"% variance")) +
        ylab(paste0("PC2: ",percentVar[2],"% variance"))

Then I decided to do a normal pca from r:     

met =assay(met)
pca<- prcomp(t(met))
idx <- seq_len(3)
print(splom(pca$x[,idx], col=col,pch=19))


Function for screeplot:

screeplot_percent <- function(x, npcs = min(10, length(x$sdev)), ...) {
  idx <- seq_len(npcs)
  sum_var <- sum(x$sdev ^ 2)
  vars <- 100 * (x$sdev[idx] ^ 2 / sum_var)
  cumvar <- cumsum(vars)
  barplot(vars, width = 0.9, space = 0.1, names.arg = idx, ylim = c(0, 100),
          xlab = "Principal Component", ylab = "Percent Variance",
          xaxp = c(1, npcs, npcs - 1), las = 1)
  lines(x = idx - 0.5, y = cumvar, type = "b", lty = 2)
  legend("bottomright", legend = c("Proportion", "Cumulative"), lty = c(1, 2),
         pch = c(19, 1))


red -> WEN1
pink -> WEN3
black -> WNN1
blue -> WNN3


In fact PCA plots differ a bit and screeplot differ a lot. However, I do not understand why. 
As you see WEN3 and WNN3 are quite apart on the second plot in comparison to the first plot. Additionally, the scale on the y-axis and x-axis is different. What is the reason for this?

Also my screeplot tells me that PC1 explains app. 75% of variance whereas ggplot claims 87%.


ADD COMMENTlink modified 18 months ago by Michael Love12k • written 18 months ago by tonja.r10
gravatar for Michael Love
18 months ago by
Michael Love12k
United States
Michael Love12k wrote:
Whenever you have a question about a function in Bioconductor, a good to start is with the help page for that function. For ?plotPCA in DESeq2, you'll see there is an extra step of filtering to use the top high variance genes.
ADD COMMENTlink written 18 months ago by Michael Love12k
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