Subtract every column from each other column in a R data.table

Question

Let\'s say I have a data.table

set.seed(1) # to make the example reproducible
ex<-data.table(AAA=runif(100000),
               BBB=runif(100000),
                 


        

Answer 1

Looping over the combinations within data.table:

comblist <- combn(names(ex)[-5],2,FUN=list)
res2 <- ex[,lapply(comblist,function(x) get(x[1])-get(x[2]))]

setnames(res2,names(res2),sapply(comblist,paste,collapse="_"))