`ifelse` function changes the type of object, how to fix it?

EconKid · November 6, 2018, 9:39am

I use ifelse function to build a udf. But I find this function change the type of R object I want.
Here I want to use arg is_tibble to give the users options to get a tibble or not.
And I expect convert_tbl(a,is_tibble = T) returns a data.frame for you, but it fails.

library(tidyverse)
a <- 
    matrix(
        1:4
        ,nrow = 2
        ,byrow = T
    )
a
#>      [,1] [,2]
#> [1,]    1    2
#> [2,]    3    4
a %>% as_tibble()
#> # A tibble: 2 x 2
#>      V1    V2
#>   <int> <int>
#> 1     1     2
#> 2     3     4
convert_tbl <- 
    function(matrix,is_tibble=F){
        ifelse(
            is_tibble==F
            ,matrix
            ,as_tibble(matrix)
        )
    }
convert_tbl(a,is_tibble = T)        
#> [[1]]
#> [1] 1 3
convert_tbl(a,is_tibble = F)
#> [1] 1

^{Created on 2018-11-06 by the reprex package (v0.2.1)}

Session info

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mishabalyasin · November 6, 2018, 11:06am

Why not use if... else instead? Documentation on ifelse says that "ifelse returns a value with the same shape as test" (emphasis mine), so it's working as intended from it's point of view. if... else doesn't have this problem:

library(tidyverse)
a <- 
  matrix(
    1:4
    ,nrow = 2
    ,byrow = TRUE
  )
a
#>      [,1] [,2]
#> [1,]    1    2
#> [2,]    3    4
a %>% as_tibble()
#> # A tibble: 2 x 2
#>      V1    V2
#>   <int> <int>
#> 1     1     2
#> 2     3     4

convert_tbl <- function(matrix,is_tibble=FALSE){
  if(is_tibble)
    as_tibble(matrix)
  else
    matrix
}
convert_tbl(a, is_tibble = TRUE)        
#> # A tibble: 2 x 2
#>      V1    V2
#>   <int> <int>
#> 1     1     2
#> 2     3     4
convert_tbl(a, is_tibble = FALSE)
#>      [,1] [,2]
#> [1,]    1    2
#> [2,]    3    4

^{Created on 2018-11-06 by the reprex package (v0.2.1)}

And not connected to your question, but couple of suggestions on coding style:

It is better to use TRUE/FALSE, not T/F. Code is read more often than written, so spare some thought to people who will read it later and seeing TRUE/FALSE is simply easier.
is_*** usually indicates a predicate, meaning function that itself will return TRUE/FALSE and not something that is TRUE/FALSE to begin with. The way you use it in your function is probably more like tibblify or convert_to_tibble or something like that.

mishabalyasin · November 6, 2018, 12:56pm

Small addition, looks like your problem with how ifelse works is annoying for not only you . There is new package from Hadley that, apparently, was motivated in part by this inconsistent behavior

https://vctrs.r-lib.org/articles/stability.html#ifelse

system · November 13, 2018, 12:56pm

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