compose returnes only output of first function 'composed'

[benjaminschwetz]

This might be identical #629, but I am afraid I don't exactly understand that issue, so posting mine to be sure.

Previously this worked

n_unique <- purrr::compose(length, unique)
       n_unique(iris$Species)
#> [1] 3

Now with 0.3.0 it returns:

n_unique <- purrr::compose(length, unique)
n_unique(iris$Species)
#> [1] setosa     versicolor virginica 
#> Levels: setosa versicolor virginica

^{Created on 2019-02-11 by the reprex package (v0.2.1)}

I read the news about the changes made to compose but in my understanding, this code should still return the same output as before.

[egnha]

Minor digression from the actual issue at hand: dplyr::n_distinct() is a faster alternative.

[romatik]

Looks like a bug since manual composition works as before (and expected)

n_unique <- purrr::compose(length, unique) 
n_unique(iris$Species)
#> [1] setosa     versicolor virginica 
#> Levels: setosa versicolor virginica

length(unique(iris$Species))
#> [1] 3

^{Created on 2019-02-11 by the reprex package (v0.2.1)}

Session info

devtools::session_info()
#> ─ Session info ──────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.5.2 (2018-12-20)
#>  os       Ubuntu 18.04.1 LTS          
#>  system   x86_64, linux-gnu           
#>  ui       X11                         
#>  language en_US                       
#>  collate  en_US.UTF-8                 
#>  ctype    en_US.UTF-8                 
#>  tz       Europe/Berlin               
#>  date     2019-02-11                  
#> 
#> ─ Packages ──────────────────────────────────────────────────────────────
#>  package     * version date       lib source                         
#>  assertthat    0.2.0   2017-04-11 [1] CRAN (R 3.5.0)                 
#>  backports     1.1.3   2018-12-14 [1] CRAN (R 3.5.1)                 
#>  callr         3.1.1   2018-12-21 [1] CRAN (R 3.5.2)                 
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#>  ps            1.3.0   2018-12-21 [1] CRAN (R 3.5.2)                 
#>  purrr         0.3.0   2019-01-27 [1] CRAN (R 3.5.2)                 
#>  R6            2.3.0   2018-10-04 [1] CRAN (R 3.5.1)                 
#>  Rcpp          1.0.0   2018-11-07 [1] CRAN (R 3.5.1)                 
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#>  yaml          2.2.0   2018-07-25 [1] CRAN (R 3.5.0)                 
#> 
#> [1] /home/misha/R/x86_64-pc-linux-gnu-library/3.5
#> [2] /usr/local/lib/R/site-library
#> [3] /usr/lib/R/site-library
#> [4] /usr/lib/R/library

[yutannihilation]

Yes, this is the same as #629... unique() is a generic funciton.

[ColinFay]

This seems to be linked to the useMethod() of unique().

The first out is a UseMethod("unique") while the second is a .Primitive("length")(x), so the x is not processed in the first function :

library(purrr)

n_unique <- purrr::compose(length, unique)
n_unique(iris$Species)
#> [1] setosa     versicolor virginica 
#> Levels: setosa versicolor virginica
body(n_unique)
#> {
#>     out <- {
#>         UseMethod("unique")
#>     }
#>     fns <- list(function (x) 
#>     .Primitive("length")(x))
#>     for (fn in fns) {
#>         out <- fn(out)
#>     }
#>     out
#> }

unique_length <- compose(unique, length)
unique_length(iris$Species)
#> [1] 150
body(unique_length)
#> {
#>     out <- {
#>         .Primitive("length")(x)
#>     }
#>     fns <- list(function (x, incomparables = FALSE, ...) 
#>     UseMethod("unique"))
#>     for (fn in fns) {
#>         out <- fn(out)
#>     }
#>     out
#> }

foo <- purrr::compose(length, as.list)
foo(head(iris, 2))
#> $Sepal.Length
#> [1] 5.1 4.9
#> 
#> $Sepal.Width
#> [1] 3.5 3.0
#> 
#> $Petal.Length
#> [1] 1.4 1.4
#> 
#> $Petal.Width
#> [1] 0.2 0.2
#> 
#> $Species
#> [1] setosa setosa
#> Levels: setosa versicolor virginica
body(foo)
#> {
#>     out <- {
#>         UseMethod("as.list")
#>     }
#>     fns <- list(function (x) 
#>     .Primitive("length")(x))
#>     for (fn in fns) {
#>         out <- fn(out)
#>     }
#>     out
#> }

bar <- purrr::compose(nrow, head)
bar(iris)
#>   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
#> 1          5.1         3.5          1.4         0.2  setosa
#> 2          4.9         3.0          1.4         0.2  setosa
#> 3          4.7         3.2          1.3         0.2  setosa
#> 4          4.6         3.1          1.5         0.2  setosa
#> 5          5.0         3.6          1.4         0.2  setosa
#> 6          5.4         3.9          1.7         0.4  setosa
body(bar)
#> {
#>     out <- {
#>         UseMethod("head")
#>     }
#>     fns <- list(function (x) 
#>     dim(x)[1L])
#>     for (fn in fns) {
#>         out <- fn(out)
#>     }
#>     out
#> }

^{Created on 2019-02-11 by the reprex package (v0.2.1)}