multivariate qqplot
===

I am trying to make qqplot for more than one variable. Here is the code I used below. Instead I  obtained a qqplot of both variables (i.e. one line plot). I want to be able to compare the observed (a1, b1) of both variables with the expected (exp) line. Will appreciate your suggestion.

    a <- read.table("/home/abc/results-qc.txt",header=T)
    b <- read.table("/home/abc/results-qc.txt",header=T)
    pdf(file="/home/abc/2qqplot.pdf")> 
    a1=-log10(a$p)
    b1=-log10(b$p) 
    n = length(a$p)
    exp = -log10(1:n/(a$p+1))
    qqplot(a1,b1, main = "Q-Q Plot mvp", xlab = "mvp2 P-values", ylab = "mvp1 P-values")
    abline(0,1, col=2)
    dev.off()

qqNbie