[R] For loop with multiple iteration indexes

Jim Lemon drj|m|emon @end|ng |rom gm@||@com
Mon Sep 10 07:16:00 CEST 2018

Hi David,
If you mean that you have two data frames named x and y and want the
correlations between the columns that would be on the diagonal of a
correlation matrix:

for(i in 1:n) r[[i]]<-cor(x[,i],y[,i])

If I'm wrong, let me know.


On Mon, Sep 10, 2018 at 3:06 PM David Disabato <ddisab01 using gmail.com> wrote:
> Hi R-help,
> I am trying to create a for loop with multiple iteration indexes. I don't
> want to use two different for loops nested together because I don't need
> the full matrix of the two indexes, just the diagonal elements (e.g., i[1]
> & j[1] and i[2] & j[2], but not i[1] & j[2]). Is there a way to specify
> both i and j in a single for loop? Here is a simplified example of
> pseudo-code where x and y are equally sized character vectors with column
> names and dat is their dataframe (obviously this code doesn't run in R, but
> hopefully you perceive my goal):
> r <- list()
> n <- 0
> for (i in x; j in y) {
>    n <- n + 1
>    r[[n]] <- cor(x = dat[, i], y = dat[, j])
> }
> print(r)
> I realize there are other solutions to this particular correlation example,
> but my actual problem is much more complicated, so I am hoping for a
> solution that generalizes across any code within the for loop.
> --
> David J. Disabato, M.A.
> Clinical Psychology Doctoral Student
> George Mason University
> ddisabat using gmu.edu
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