This is an R Version 3.4.4 question
A voting function voteOnBase, takes 2 arguments and returns a 2-element list: the WINNER and the VOTE.COUNT. I want to use it to add those two columns to notVotedYet, a tibble. The following code runs correctly.
library(tidyverse)
withVotes <- notVotedYet %>%
group_by(BASE) %>%
mutate(WINNER = voteOnBase(BASE, CODES)[[1]],
VOTE.COUNT = voteOnBase(BASE, CODES)[[2]])
However, it calls voteOnBase twice on the same inputs. How can I eliminate the extra function call but still add the same two columns?
Not easy to answer without some example data and output, but I would suggest writing voteOnBase() to return a tibble, not a list. Then you can store the result in a list column and create the columns using unnest().
To illustrate: here's a function, square_it() which like yours, takes 2 arguments and returns 2 elements - but as columns in a tibble.
square_it <- function(x, y) {
tibble(x = x^2, y = y^2)
}
We can use the iris dataset to pass the arguments. We use pmap() to specify the variables and the function. The list column is named sq:
iris %>%
as_tibble() %>%
mutate(sq = pmap(list(Sepal.Length, Sepal.Width), square_it))
# A tibble: 150 x 6
Sepal.Length Sepal.Width Petal.Length Petal.Width Species sq
<dbl> <dbl> <dbl> <dbl> <fct> <list>
1 5.1 3.5 1.4 0.2 setosa <tibble [1 x 2]>
2 4.9 3 1.4 0.2 setosa <tibble [1 x 2]>
3 4.7 3.2 1.3 0.2 setosa <tibble [1 x 2]>
4 4.6 3.1 1.5 0.2 setosa <tibble [1 x 2]>
5 5 3.6 1.4 0.2 setosa <tibble [1 x 2]>
6 5.4 3.9 1.7 0.4 setosa <tibble [1 x 2]>
7 4.6 3.4 1.4 0.3 setosa <tibble [1 x 2]>
8 5 3.4 1.5 0.2 setosa <tibble [1 x 2]>
9 4.4 2.9 1.4 0.2 setosa <tibble [1 x 2]>
10 4.9 3.1 1.5 0.1 setosa <tibble [1 x 2]>
# ... with 140 more rows
Just add %>% unnest(sq) to that code, to generate the columns x and y:
iris %>%
as_tibble() %>%
mutate(sq = pmap(list(Sepal.Length, Sepal.Width), square_it)) %>%
unnest(sq)
# A tibble: 150 x 7
Sepal.Length Sepal.Width Petal.Length Petal.Width Species x y
<dbl> <dbl> <dbl> <dbl> <fct> <dbl> <dbl>
1 5.1 3.5 1.4 0.2 setosa 26.0 12.2
2 4.9 3 1.4 0.2 setosa 24.0 9
3 4.7 3.2 1.3 0.2 setosa 22.1 10.2
4 4.6 3.1 1.5 0.2 setosa 21.2 9.61
5 5 3.6 1.4 0.2 setosa 25 13.0
6 5.4 3.9 1.7 0.4 setosa 29.2 15.2
7 4.6 3.4 1.4 0.3 setosa 21.2 11.6
8 5 3.4 1.5 0.2 setosa 25 11.6
9 4.4 2.9 1.4 0.2 setosa 19.4 8.41
10 4.9 3.1 1.5 0.1 setosa 24.0 9.61
# ... with 140 more rows