Dataframe create new column based on other columns

Question

I have a dataframe:

df <- data.frame(\'a\'=c(1,2,3,4,5), \'b\'=c(1,20,3,4,50))
df
    a    b
1   1    1
2   2   20
3   3    3
4   4    4
5   5   50
         


        

Answer 1

Here is a slightly more confusing algebraic method:

df$c <- with(df, b + ((-1)^((a==b)+1) * a))

df
  a  b  c
1 1  1  2
2 2 20 18
3 3  3  6
4 4  4  8
5 5 50 45

The idea is that the "minus" operator is turned on or off based on the test a==b.