I've been testing out the vctrs package recently, especially what they call "record-style" objects recently, and I'm wondering if there's any way to get them to play nice with dplyr::mutate. Currently, when dplyr::mutate gives me an error about the length of the objects whenever I try to use them.
I don't know of a built in type that's appropriate, so as a reprex I'm going to use the rational class described in this vignette.
library("vctrs")
library("dplyr")
new_rational <- function(n = integer(), d = integer()) {
vec_assert(n, ptype = integer())
vec_assert(d, ptype = integer())
new_rcrd(list(n = n, d = d), class = "vctrs_rational")
}
format.vctrs_rational <- function(x, ...) {
n <- field(x, "n")
d <- field(x, "d")
out <- paste0(n, "/", d)
out[is.na(n) | is.na(d)] <- NA
out
}
So far so good, but when I try to create a column of rationals using dplyr::mutate I get an error
df <- data.frame(n = c(1L, 2L, 3L), d = 2L)
df %>% dplyr::mutate(frac = new_rational(n, d))
#> Error: Column `frac` must be length 3 (the number of rows) or one, not 2
But creating the column in base R works just fine:
df$rational <- new_rational(df$n, df$d)
df
#> n d rational
#> 1 1 2 1/2
#> 2 2 2 2/2
#> 3 3 2 3/2
Is there some trick to get this to work using dplyr::mutate, or is this just not possible?
new_rational returns the output in a list format as you can see below
> typeof(new_rational(n=1L, d=2L))
[1] "list"
so, we can get the output as a list using map or as.list "@Ronak's suggestion" then use unnest.
df %>% dplyr::mutate(frac = purrr::map2(n,d, ~new_rational(.x, .y))) %>%
tidyr::unnest(cols=c(frac))
# A tibble: 3 x 3
n d frac
<int> <int> <vctrs_rt>
1 1 2 1/2
2 2 2 2/2
3 3 2 3/2