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In summarise draws, a function that returns a character changes all columns to character #355

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n-kall opened this issue Mar 14, 2024 · 4 comments · May be fixed by #356
Open

In summarise draws, a function that returns a character changes all columns to character #355

n-kall opened this issue Mar 14, 2024 · 4 comments · May be fixed by #356

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@n-kall
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n-kall commented Mar 14, 2024 •
edited

If a summary function that returns a character is used in summarise_draws, it makes all columns <chr> which messes up formatting.

example_draws() |>
   summarise_draws(x, char_fun = \(x) "word", mean)

Returns

# A tibble: 10 × 3
   variable char_fun      mean
   <chr>    <chr>         <chr>
 1 mu       word          4.1799990610081
 2 tau      word          4.16356885610418
 3 theta[1] word          6.74893947963962
 4 theta[2] word          5.25331634990726
 5 theta[3] word          3.04393475572924
 6 theta[4] word          4.85842854299997
 7 theta[5] word          3.22258991784476
 8 theta[6] word          3.98696993634695
 9 theta[7] word          6.5030995214442
10 theta[8] word          4.56520199862817

This could be fixed by using type.convert(out, as.is = TRUE) on the output tibble in summarise_draws_helper
@mjskay
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mjskay commented Mar 14, 2024

This suggests to me that the output is being bound into a matrix (which requires a single type) and then converted to a data frame later, which it should probably not be. Rather than potentially round-tripping through a string (with the possibility for information loss) I would suggest binding results together into a data frame directly, which should be more efficient anyway.

@n-kall
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n-kall commented Mar 14, 2024

This suggests to me that the output is being bound into a matrix

Yes, this is indeed the case

@paul-buerkner
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paul-buerkner commented Mar 14, 2024 via email

@n-kall
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n-kall commented Mar 15, 2024

It seems this is also caused by the behaviour of unlist, which results in a vector, and when performed on a list with different types inside, will convert them all to the same (in this case character). This unlisting is done to handle summary functions that return multiple elements (e.g. quantile2).

However, I don't know of a base R equivalent to purrr::flatten which would do what we want in this case (returning a list, but without nesting).

@n-kall n-kall linked a pull request Mar 15, 2024 that will close this issue
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@avehtari avehtari mentioned this issue May 10, 2024
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modify summarise_draws internals not to coerce values to same type n-kall/posterior
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@mjskay @paul-buerkner @n-kall