Devel vctrs::vec_rbind does not remove column names in list columns

[colearendt]

This is breaking behavior for https://github.com/colearendt/tidyjson, so wanted to report it. It is not clear to me whether this is an intentional or unintentional change in behavior. It seems marginally related to #999 and #966.

As I think about this behavior, it seems almost desirable to keep the names - it was not clear to me why names were dropped in the first place (but we do depend on it in a few places, for better or worse. Others may as well).

I originally noticed the behavior in tidyr::unnest() and traced it here:

original behavior

Notice that chr "b" is not named

packageVersion("vctrs")
#> [1] '0.2.4'
hm <- tibble::tibble(col = list(a = "b"))
str(vctrs::vec_rbind(hm, .ptype = NULL))
#> tibble [1 × 1] (S3: tbl_df/tbl/data.frame)
#>  $ col:List of 1
#>   ..$ : chr "b"

^{Created on 2020-04-13 by the reprex package (v0.3.0)}

devel behavior

Notice that chr "b" retains its name

packageVersion("vctrs")
#> [1] '0.2.99.9011'
hm <- tibble::tibble(col = list(a = "b"))
str(vctrs::vec_rbind(hm, .ptype = NULL))
#> tibble [1 × 1] (S3: tbl_df/tbl/data.frame)
#>  $ col:List of 1
#>   ..$ a: chr "b"

^{Created on 2020-04-13 by the reprex package (v0.3.0)}

[lionel-]

This is intended behaviour, the inner names are now correctly kept.

[colearendt]

Thanks! Do you know why the legacy behavior existed? Is this the behavior that rbind has or something?

[hadley]

It's what data.frame does:

data.frame(x = 1:2, y = c(a = 1, b = 2))$y
#> [1] 1 2

^{Created on 2020-04-13 by the reprex package (v0.3.0)}

(But I now think that's tangled up with how data frames convert the names of the first column to row names)

[lionel-]

It was because we used vec_assign() (our equivalent of [<-) to fill a pre-initalised vector, and nor vec-assign neither [<- copy over names / inner names. Now our internal version of vec-assign has a parameter to allow copying the names.

[colearendt]

Awesome, that background is super helpful, thanks! Is it worth noting this as a change / breaking change? It was a hard one to trace down, although perhaps it is unusual for someone to depend on something not having names.

[lionel-]

The NEWS item is now in a breaking change section, thanks for the report!