Hi all,

I'm looking for a function with the same functionalities as Hmisc::summarize
but accepting a dataframe as input (not just a vector or a matrix).
I'd like to compute the correlation between two variables in my dataframe,
grouped according to other variables in the same dataframe.

For exemple, consider the following dataframe D:
V1  V2   V3
A     1    -1
A     1     1
A    -1    -1
B     1     1
B     1     1

I'd like to use Hmisc::summarize(X=D, llist(myvar=D$V1), FUN=corr.V2.V3)

where corr.V2.V3 is defined as follows:

corr.V2.V3 = function(x) {
  d = as.data.frame(x)

  out = c(cor(d$V2, d$V3))
  names(out) = c("CORR")
  return(out)
}


As I was not able to use the Hmisc::summarize in this case, I wrote a
function using sapply instead (to construct the output dataframe), but this
is much less practical.

Thanks in advance,
Arnaud

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