CODEWITHSUNDEEP
rdplyr
banbh
banbh

Reputation: 1535

Combine columns into list column

Is there a more tidyverse-idiomatic way to combine several columns into a list column than using mapply?

For example given the following

tibble(.rows = 9) %>% 
  mutate(foo = runif(n()),
         a_1 = runif(n()),
         a_2 = runif(n()),
         a_3 = runif(n())) ->
  Z

(where Z might contain other columns, and might also contain more than 3 as) one can do

Z %>% mutate(A = mapply(c, a_1, a_2, a_3, SIMPLIFY = FALSE))

which works fine, although it would be nice to be able to say starts_with('a_') instead of a_1, a_2, a_3.

Another possibility is

Z %>% 
  rowid_to_column() %>% 
  pivot_longer(cols = starts_with('a_')) %>% 
  group_by(rowid) %>% 
  summarise(foo = unique(foo),
            A = list(value)) %>% 
  select(-rowid)

which technically works, but introduces other problems (e.g., it uses an ugly foo = unique(foo); furthermore if instead of just one foo there were many foos it would become a bit more involved).

Upvotes: 4

Views: 2531

Answers (1)

koenniem
koenniem

Reputation: 576

Based on a previous answer (now deleted) and the comments, I made a comparison of different solutions:

FUN_mapply <- function() {  Z %>% mutate(A = mapply(c, a_1, a_2, a_3, SIMPLIFY = FALSE)) }
FUN_asplit <- function() { Z %>% mutate(A = asplit(.[,grepl("^a", colnames(.))], 1))  }
FUN_pmap <- function() { Z %>% mutate(A = pmap(.[,grepl("^a", colnames(.))], c)) }
FUN_transpose <- function() { Z %>% mutate(A = transpose(.[,grepl("^a", colnames(.))])) }
FUN_asplit_tidy <- function() { Z %>% mutate(A = asplit(select(., starts_with("a")), 1))  }
FUN_pmap_tidy <- function() { Z %>% mutate(A = pmap(select(., starts_with("a")), c)) }
FUN_transpose_tidy <- function() { Z %>% mutate(A = transpose(select(., starts_with("a")))) }

all(unlist(pmap(list(FUN_mapply()$A, FUN_asplit()$A, FUN_pmap()$A, FUN_transpose()$A), ~all(mapply(all.equal, .x, .y, MoreArgs = list(attributes = F)))))) # All A columns are equal?

mb <- microbenchmark::microbenchmark(
    FUN_mapply(),
    FUN_asplit(),
    FUN_pmap(),
    FUN_transpose(),
    FUN_asplit_tidy(), 
    FUN_pmap_tidy(), 
    FUN_transpose_tidy(), 
    times = 1000L
)

ggplot2::autoplot(mb)

enter image description here

Edit: Replace select(., starts_with("a")) with Z[,grepl("^a", colnames(Z))]

Upvotes: 7

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