How do I get a contingency table?

Question

I am trying to create a contingency table from a particular type of data. This would be doable with loops etc... but because my final table would contain more than 10E5 cell

Answer 1

Simply use dcast() function of "reshape2" package:

ans = dcast( df, PLANT~ ANIMAL,value.var = "INTERACTIONS", fill = 0 ) 

Here "PLANT" will be on the left column, "ANIMALS" on the top row, filling of the table will happen using "INTERACTIONS" and "NULL" values will be filled using 0's.