In the R language, given tables in matrix, data.frame or data.table classe, I did not find a safe way to extract a column whose position is given by a variable. The multi-element operator pattern [, i] will not work out of the box in data.table, which expects [,i,with=F] instead, and the single-element operator pattern [[i]] will not work with matrices, which will return their ith element. Is there another operator that will extract safely a column over multiple classes of tables ? #Rstats