Dplyr mutating using another dataframe

Question

Say I want to mutate a column ev1 for stim1 by finding the corresponding number in the Stimuli dataframe and finding its reward. For example

stim1 in data looks like this

Stimuli looks like this

    number    reward
1        0 0.0000000
2        1 0.3333333
3        2 0.6666667
4        3 1.0000000...

Desired outcome

  stim1   ev1
1     2    0.6666667
2     1    0.3333333
3     3    1.0000000
4     2    0.6666667
5     1    0.3333333

My attempt of

data %>%  
  mutate(ev1=Stimuli$reward[which(Reward$number==stim1)]) -> data_modified

yields an error. Any help would be greatly appreciated!

How does the second row of stim1 from 4 become 1 and the fourth from 5 to 2? — s__, Aug 17 '21 at 07:44
that was a typo, thank you for pointing that out! just edited it — user15791858, Aug 17 '21 at 08:14

score 1 · Accepted Answer · answered Aug 17 '21 at 08:17

We could do a left_join:

left_join() returns all rows from x, and all columns from x and y. Rows in x with no match in y will have NA values in the new columns. If there are multiple matches between x and y, all combinations of the matches are returned.

library(dplyr)
left_join(stim1, Stimuli, by=c("stim1"="number"))

Output:

stim1    reward
1     2 0.6666667
2     1 0.3333333
3     3 1.0000000
4     2 0.6666667
5     1 0.3333333

Dplyr mutating using another dataframe

1 Answers1