Is there a function like switch which works inside of dplyr::mutate?

Question

I can't use switch inside of mutate because it returns the whole vector instead of just the row. As a hack, I'm using:

pick <- function(x, v1, v2, v3, v4) {     ifelse(x == 1, v1,            ifelse(x == 2, v2,                   ifelse(x == 3, v3,                          ifelse(x == 4, v4, NA)))) } 

This works inside of mutate, and is fine for now because I'm typically choosing among 4 things, but that may change. Can you recommend an alternative?

For example:

library(dplyr) df.faithful <- tbl_df(faithful) df.faithful$x  <- sample(1:4, 272, rep=TRUE) df.faithful$y1 <- rnorm(n=272, mean=7, sd=2) df.faithful$y2 <- rnorm(n=272, mean=5, sd=2) df.faithful$y3 <- rnorm(n=272, mean=7, sd=1) df.faithful$y4 <- rnorm(n=272, mean=5, sd=1) 

Using pick:

mutate(df.faithful, y = pick(x, y1, y2, y3, y4)) Source: local data frame [272 x 8]     eruptions waiting x        y1        y2       y3       y4        y 1      3.600      79 1  8.439092 5.7753006 8.319372 5.078558 8.439092 2      1.800      54 2 13.515956 6.1971512 6.343157 4.962349 6.197151 3      3.333      74 4  7.693941 6.8973365 5.406684 5.425404 5.425404 4      2.283      62 4 12.595852 6.9953995 7.864423 3.730967 3.730967 5      4.533      85 3 11.952922 5.1512987 9.177687 5.511899 9.177687 6      2.883      55 3  7.881350 1.0289711 6.304004 3.554056 6.304004 7      4.700      88 4  8.636709 6.3046198 6.788619 5.748269 5.748269 8      3.600      85 1  8.027371 6.3535056 7.152698 7.034976 8.027371 9      1.950      51 1  5.863370 0.1707758 5.750440 5.058107 5.863370 10     4.350      85 1  7.761653 6.2176610 8.348378 1.861112 7.761653 ..       ...     ... .       ...       ...      ...      ...      ... 

We see that I copy the value from y1 into y if x == 1, and so on. This is what I'm looking to do, but want to be able to do it, whether I have a list of 4 or 400 columns.

Trying to use switch:

mutate(df.faithful, y = switch(x, y1, y2, y3, 4))  Error in switch(c(1L, 2L, 4L, 4L, 3L, 3L, 4L, 1L, 1L, 1L, 4L, 3L, 1L,  :  EXPR must be a length 1 vector 

Trying to use list:

mutate(df.faithful, y = list(y1, y2, y3, y4)[[x]]) Error in list(c(8.43909205142925, 13.5159559591257, 7.69394050059568,  :  recursive indexing failed at level 2 

Trying to use c:

mutate(df.faithful, y = c(y1, y2, y3, y4)[x]) Source: local data frame [272 x 8]     eruptions waiting x        y1        y2       y3       y4         y 1      3.600      79 1  8.439092 5.7753006 8.319372 5.078558  8.439092 2      1.800      54 2 13.515956 6.1971512 6.343157 4.962349 13.515956 3      3.333      74 4  7.693941 6.8973365 5.406684 5.425404 12.595852 4      2.283      62 4 12.595852 6.9953995 7.864423 3.730967 12.595852 5      4.533      85 3 11.952922 5.1512987 9.177687 5.511899  7.693941 6      2.883      55 3  7.881350 1.0289711 6.304004 3.554056  7.693941 7      4.700      88 4  8.636709 6.3046198 6.788619 5.748269 12.595852 8      3.600      85 1  8.027371 6.3535056 7.152698 7.034976  8.439092 9      1.950      51 1  5.863370 0.1707758 5.750440 5.058107  8.439092 10     4.350      85 1  7.761653 6.2176610 8.348378 1.861112  8.439092 ..       ...     ... .       ...       ...      ...      ...       ... 

No errors are produced, but the behavior is not as intended.

Answer 1

Eons too late for the OP, but in case this shows up in a search ...

dplyr v0.5 has recode(), a vectorized version of switch(), so

data_frame(   x = sample(1:4, 10, replace=TRUE),   y1 = rnorm(n=10, mean=7, sd=2),   y2 = rnorm(n=10, mean=5, sd=2),   y3 = rnorm(n=10, mean=7, sd=1),   y4 = rnorm(n=10, mean=5, sd=1) ) %>% mutate(y = recode(x,y1,y2,y3,y4)) 

produces, as anticipated:

# A tibble: 10 x 6        x        y1       y2       y3       y4        y    <int>     <dbl>    <dbl>    <dbl>    <dbl>    <dbl> 1      2  6.950106 6.986780 7.826778 6.317968 6.986780 2      1  5.776381 7.706869 7.982543 5.048649 5.776381 3      2  7.315477 2.213855 6.079149 6.070598 2.213855 4      3  7.461220 5.100436 7.085912 4.440829 7.085912 5      3  5.780493 4.562824 8.311047 5.612913 8.311047 6      3  5.373197 7.657016 7.049352 4.470906 7.049352 7      2  6.604175 9.905151 8.359549 6.430572 9.905151 8      3 11.363914 4.721148 7.670825 5.317243 7.670825 9      3 10.123626 7.140874 6.718351 5.508875 6.718351 10     4  5.407502 4.650987 5.845482 4.797659 4.797659 

(Also works with named args, including character and factor x's.)