Why result of purrr::compose(round, mean)(1:28) differ from round(mean(1:28))?

[shizidushu]

purrr::compose(round, mean)(1:28)
#> [1] 14.5
round(mean(1:28))
#> [1] 14

^{Created on 2019-03-15 by the reprex package (v0.2.1)}

Session info

devtools::session_info()
#> Warning in system("timedatectl", intern = TRUE): running command
#> 'timedatectl' had status 1
#> ─ Session info ──────────────────────────────────────────────────────────
#>  setting  value                       
#>  version  R version 3.5.2 (2018-12-20)
#>  os       Debian GNU/Linux 9 (stretch)
#>  system   x86_64, linux-gnu           
#>  ui       X11                         
#>  language (EN)                        
#>  collate  en_US.UTF-8                 
#>  ctype    en_US.UTF-8                 
#>  tz       Etc/UTC                     
#>  date     2019-03-15                  
#> 
#> ─ Packages ──────────────────────────────────────────────────────────────
#>  package     * version date       lib source        
#>  assertthat    0.2.0   2017-04-11 [1] CRAN (R 3.5.2)
#>  backports     1.1.3   2018-12-14 [1] CRAN (R 3.5.2)
#>  callr         3.1.1   2018-12-21 [1] CRAN (R 3.5.2)
#>  cli           1.0.1   2018-09-25 [1] CRAN (R 3.5.2)
#>  crayon        1.3.4   2017-09-16 [1] CRAN (R 3.5.2)
#>  desc          1.2.0   2018-05-01 [1] CRAN (R 3.5.2)
#>  devtools      2.0.1   2018-10-26 [1] CRAN (R 3.5.2)
#>  digest        0.6.18  2018-10-10 [1] CRAN (R 3.5.2)
#>  evaluate      0.12    2018-10-09 [1] CRAN (R 3.5.2)
#>  fs            1.2.6   2018-08-23 [1] CRAN (R 3.5.2)
#>  glue          1.3.0   2018-07-17 [1] CRAN (R 3.5.2)
#>  highr         0.7     2018-06-09 [1] CRAN (R 3.5.2)
#>  htmltools     0.3.6   2017-04-28 [1] CRAN (R 3.5.2)
#>  knitr         1.21    2018-12-10 [1] CRAN (R 3.5.2)
#>  magrittr      1.5     2014-11-22 [1] CRAN (R 3.5.2)
#>  memoise       1.1.0   2017-04-21 [1] CRAN (R 3.5.2)
#>  pkgbuild      1.0.2   2018-10-16 [1] CRAN (R 3.5.2)
#>  pkgload       1.0.2   2018-10-29 [1] CRAN (R 3.5.2)
#>  prettyunits   1.0.2   2015-07-13 [1] CRAN (R 3.5.2)
#>  processx      3.2.1   2018-12-05 [1] CRAN (R 3.5.2)
#>  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 3.5.2)
#>  Rcpp          1.0.0   2018-11-07 [1] CRAN (R 3.5.2)
#>  remotes       2.0.2   2018-10-30 [1] CRAN (R 3.5.2)
#>  rlang         0.3.1   2019-01-08 [1] CRAN (R 3.5.2)
#>  rmarkdown     1.11    2018-12-08 [1] CRAN (R 3.5.2)
#>  rprojroot     1.3-2   2018-01-03 [1] CRAN (R 3.5.2)
#>  sessioninfo   1.1.1   2018-11-05 [1] CRAN (R 3.5.2)
#>  stringi       1.2.4   2018-07-20 [1] CRAN (R 3.5.2)
#>  stringr       1.3.1   2018-05-10 [1] CRAN (R 3.5.2)
#>  testthat      2.0.1   2018-10-13 [1] CRAN (R 3.5.2)
#>  usethis       1.4.0   2018-08-14 [1] CRAN (R 3.5.2)
#>  withr         2.1.2   2018-03-15 [1] CRAN (R 3.5.2)
#>  xfun          0.4     2018-10-23 [1] CRAN (R 3.5.2)
#>  yaml          2.2.0   2018-07-25 [1] CRAN (R 3.5.2)
#> 
#> [1] /usr/local/lib/R/site-library
#> [2] /usr/local/lib/R/library

[FvD]

I tried out your examples, but get the expected result in both cases:

> purrr::compose(round, mean)(1:28)
[1] 14
> round(mean(1:28))
[1] 14

[mishabalyasin]

You probably need to update your purrr to the latest version because of this bug: https://github.com/tidyverse/purrr/issues/639

[shizidushu]

@mishabalyasin Thanks. After install development version of purrr, it works.