How to use R for same field aggregation by multiple separate group

Question

I\'m trying to perform count of an indicator on several (actually hundreds) groups separately (NOT on all combinations of all groups). I\'ll demonstrate it by simplified exa

Answer 1

melt from "reshape2" has a method for matrices which could be useful here. Using "reshape2", the solution could be as straightforward as:

library(reshape2)
dcast(cbind(some_indicator, melt(data)), 
      value ~ Var2, value.var= "some_indicator", 
      fun.aggregate=sum)
#   value 1 2 3
# 1     1 1 1 0
# 2     2 2 1 1
# 3     3 0 1 2

This answer assumes some prior knowledge of how melt works on a matrix, in particular that it will create a three-column data.frame with "Var1" representing the rownames (or numbers), "Var2" representing the colnames (or numbers), and "value" representing the values from the matrix.