R: t-test over all columns

Question

I tried to do t-test to all columns (two at a time) of my data frame, and extract only the p-value. Here is what I have come up with:

for (i in c(5:525) ) {
         


        

Answer 1

Assuming your data frame looks something like this:

df = data.frame(a=runif(100),
                b=runif(100),
                c=runif(100),
                d=runif(100),
                e=runif(100),
                f=runif(100))

the the following

tests = lapply(seq(1,length(df),by=2),function(x){t.test(df[,x],df[,x+1])})

will give you tests for each set of columns. Note that this will only give you a t.test for a & b, c & d, and e & f. if you wanted a & b, b & c, c & d, d & e, and e & f, then you would have to do:

tests = lapply(seq(1,(length(df)-1)),function(x){t.test(df[,x],df[,x+1])})      

finally if let's say you only want the P values from your tests then you can do this:

pvals = sapply(tests, function(x){x$p.value})

If you are not sure how to work with an object, try typing summary(tests), and str(tests[[1]]) - in this case test is a list of htest objects, and you want to know the structure of the htest object, not necessarily the list.

Hope this helped!