write_csv only saves first column of matrix-columns in tibbles

[Aariq]

Just like list-columns in tibbles, you can create a tibble with a column that itself is a matrix. Trying to write a tibble with a list-column to a .csv throws an error, but a matrix-column does not. Only the first column of the matrix is saved though. This should probably either throw an error or save all the columns of the matrix-column.

library(tibble)
library(readr)
my_matrix <- matrix(rnorm(100), nrow = 10)
tbl <- tibble(x = letters[1:10], mat_col = my_matrix)
tbl
#> # A tibble: 10 x 2
#>    x     mat_col[,1]    [,2]   [,3]    [,4]    [,5]   [,6]    [,7]    [,8]
#>    <chr>       <dbl>   <dbl>  <dbl>   <dbl>   <dbl>  <dbl>   <dbl>   <dbl>
#>  1 a         -0.233   1.55   -0.450 -0.0861 -1.21   -1.67  -0.594   0.125 
#>  2 b          0.216  -0.393  -2.38  -0.959  -0.357  -0.130 -0.635  -1.21  
#>  3 c          0.436  -0.0963  1.17   0.813  -0.607  -1.30  -0.129   0.708 
#>  4 d         -0.0352 -1.08   -1.08  -1.14    0.824  -2.17   0.754  -0.432 
#>  5 e          1.04   -0.614  -1.35  -2.04   -1.30   -0.628 -0.782  -0.0613
#>  6 f         -1.16    0.282  -0.702 -1.20   -0.869   0.174  0.0553  1.10  
#>  7 g          0.812   0.359  -0.409  3.07    0.258  -1.03   0.478   0.882 
#>  8 h         -0.573  -0.547  -0.327  0.484   0.0848  0.470 -1.35    0.226 
#>  9 i         -0.113   0.247   1.54  -0.234  -1.25    1.01  -0.194  -0.357 
#> 10 j         -0.0136  0.599  -0.464 -0.513   1.73    0.494  0.696  -0.698 
#> # … with 2 more variables: [,9] <dbl>, [,10] <dbl>
write_csv(tbl, "test.csv")
read_csv("test.csv")
#> 
#> ── Column specification ────────────────────────────────────────────────────────
#> cols(
#>   x = col_character(),
#>   mat_col = col_double()
#> )
#> # A tibble: 10 x 2
#>    x     mat_col
#>    <chr>   <dbl>
#>  1 a     -0.233 
#>  2 b      0.216 
#>  3 c      0.436 
#>  4 d     -0.0352
#>  5 e      1.04  
#>  6 f     -1.16  
#>  7 g      0.812 
#>  8 h     -0.573 
#>  9 i     -0.113 
#> 10 j     -0.0136

^{Created on 2021-01-11 by the reprex package (v0.3.0)}