Question

Ok, the title may not be the most descriptive. It’s easier to explain with an example.

I have a data.frame like this:

A B 1 2
L M 3 0
P Q 5 6

I want to output an array of the cell in column 1 if col3 > col4, or the cell in col2 if col3 <= col4. The output vector from this data.frame would be B, L, Q.

I’m aware that I still haven’t explained my problem very well, so here is what it would look like in an imperative language:

vector = []
for each rows as row
  if row[3] > row[4]
    vector.add(row[1])
  else
    vector.add(row[2])
return vector

I apologise if this problem has already been answered, but unfortunately Google is not much of help when it comes to R questions.

Thanks,
Andreas

Answer 1

This should work (assuming df is your data frame)

apply(df, 1, function(x){ifelse(x[3] > x[4], x[1], x[2])})