How can I use one column to determine where I get the value for another column?

Question

I\'m trying to use one column to determine which column to use as the value for another column It looks something like this:

     X   Y  Z   Target
1    a   b           


        

Answer 1

You could try apply rowwise like this:

transform(df, TargetValue = apply(df, 1, function(x) x[x["Target"]]))
#   X Y Z Target TargetValue
# 1 a b c      X           a
# 2 d e f      Y           e
# 3 g h i      Z           i