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

Try this one

X <- rnorm(n=50, mean = 10, sd = 5)
Y <- rnorm(n=50, mean = 15, sd = 6)
Z <- rnorm(n=50, mean = 20, sd = 5)
Data <- data.frame(X, Y, Z)

library(plyr)

combos <- combn(ncol(Data),2)

adply(combos, 2, function(x) {
  test <- t.test(Data[, x[1]], Data[, x[2]])

  out <- data.frame("var1" = colnames(Data)[x[1]]
                    , "var2" = colnames(Data[x[2]])
                    , "t.value" = sprintf("%.3f", test$statistic)
                    ,  "df"= test$parameter
                    ,  "p.value" = sprintf("%.3f", test$p.value)
                    )
  return(out)

})



  X1 var1  var2 t.value       df p.value
1  1   X      Y  -5.598 92.74744   0.000
2  2   X      Z  -9.361 90.12561   0.000
3  3   Y      Z  -3.601 97.62511   0.000