Applying a function to every combination of two columns in a dataframe using R -

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i want apply function myfooto every possible combination of 2 columns in dataframe mydf , result in matrix format myoutput.

consider following dataframe,

# example dataframe mydf <- data.frame(var1 = 1:10, var2 = 11:20, var3 = 21:30) head(mydf)  # var1 var2 var3 # 1    11   21 # 2    12   22 # 3    13   23 # 4    14   24 # 5    15   25

to want apply following function every possible combination of 2 columns,

# example function myfoo <- function(vara, varb) sum(vara * varb)  myfoo(var1, var2) # [1] 935

in order output.

# desired output myoutput <- matrix(c(0, 935, 1485, 935, 0, 4035, 1485, 4035, 0), 3, dimnames = list(names(mydf), names(mydf))) myoutput  #      var1 var2 var3 # var1    0  935 1485 # var2  935    0 4035 # var3 1485 4035    0

in case convert matrix (no reason keep data.frame when columns of numeric class) , run compiled crossprod function matrix cross product.

m <- as.matrix(mydf) res <- crossprod(m, m) diag(res) <- 0 # can skip part res #      var1 var2 var3 # var1    0  935 1485 # var2  935    0 4035 # var3 1485 4035    0

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