Better naming options for pack()

[mgirlich]

I like the idea of pack and unpack, especially as they sometimes come quite natural when working with JSON data from APIs. In such a case I might want to unpack a tibble column, manipulate it and pack it afterwards again. E.g.

library(tidyr)
api_data <- tibble(
  Sepal = tibble(
    Length = c(5.1, 4.7),
    Width = c(3.5, 3.2)
  ),
  Petal = tibble(
    Length = c(1.4, 1.3),
    Width = c(0.2, 0.2)
  )
)

data_to_work_with <- api_data %>% 
  unpack(c(Sepal, Petal), names_sep = ".")

# some data manipulation

data_to_work_with %>% 
  pack(Sepal = starts_with("Sepal"))
#> # A tibble: 2 x 3
#>   Petal.Length Petal.Width Sepal$Sepal.Length $Sepal.Width
#>          <dbl>       <dbl>              <dbl>        <dbl>
#> 1          1.4         0.2                5.1          3.5
#> 2          1.3         0.2                4.7          3.2

^{Created on 2019-10-30 by the reprex package (v0.3.0)}

Unfortunately, this repacking step isn't supported very nicely as I cannot change the names in the step of packing. I would imagine something along the following lines to be possible:

data_to_work_with %>% 
  pack(Sepal = c(Length = Sepal.Length, Width = Sepal.Width))

data_to_work_with %>% 
  pack(Sepal = c(Sepal.Length, Width = Width), .prefix = "Sepal.")

The first case is especially confusing as the names are simply ignored without a warning.

[hadley]

Slightly more straightforward reprex:

library(tidyr)

iris %>% 
  as_tibble() %>% 
  pack(Sepal = starts_with("Sepal"), Petal = starts_with("Petal"))
#> # A tibble: 150 x 3
#>    Species Sepal$Sepal.Length $Sepal.Width Petal$Petal.Length $Petal.Width
#>    <fct>                <dbl>        <dbl>              <dbl>        <dbl>
#>  1 setosa                 5.1          3.5                1.4          0.2
#>  2 setosa                 4.9          3                  1.4          0.2
#>  3 setosa                 4.7          3.2                1.3          0.2
#>  4 setosa                 4.6          3.1                1.5          0.2
#>  5 setosa                 5            3.6                1.4          0.2
#>  6 setosa                 5.4          3.9                1.7          0.4
#>  7 setosa                 4.6          3.4                1.4          0.3
#>  8 setosa                 5            3.4                1.5          0.2
#>  9 setosa                 4.4          2.9                1.4          0.2
#> 10 setosa                 4.9          3.1                1.5          0.1
#> # … with 140 more rows

^{Created on 2019-11-24 by the reprex package (v0.3.0)}

Maybe this could be achieved by

iris %>% 
  as_tibble() %>% 
  pack(
    Sepal = starts_with("Sepal"), 
    Petal = starts_with("Petal"), 
    .names_sep = "."
)

Since you'd still want some way to strip the .. names_sep = NULL would remain the default, but names_sep would just remove the outer name from the inner name.

[dah33]

One suggestion is a .names_prefix argument, similar to pivot_longer():

iris %>% 
  as_tibble() %>% 
  pack(
    Sepal = starts_with("Sepal"), 
    Petal = starts_with("Petal"), 
    .names_prefix = "(Sepal|Petal)\\."
  )

Although I note a couple of issues:

• The use of regexp in the the prefix pattern could potentially be confusing, as "." is a common separator, but has a non-literal meaning in regexp.
• The pack function could be more helpful, since it has already been given the variable name patterns start with Sepal and Petal.

Another approach would extend Hadley's:

iris %>% 
  as_tibble() %>% 
  pack(
    Sepal = starts_with("Sepal"), 
    Petal = starts_with("Petal"), 
    .names_sep = "."
)

To this:

iris %>% 
  as_tibble() %>% 
  pack(c(Sepal, Petal), names_sep = ".")

So the starts_with() are inferred. This would work as a natural complement of unpack():

iris %>% 
  as_tibble() %>% 
  pack(c(Sepal, Petal), names_sep = ".") %>%
  unpack(c(Sepal, Petal), names_sep = ".")

The pack() step above would give this result:

tibble(
  Species = iris$Species, 
  Sepal = tibble(Length = iris$Sepal.Length, Width = iris$Sepal.Width),
  Petal = tibble(Length = iris$Petal.Length, Width = iris$Petal.Width)
) # %>% unpack(c(Sepal, Petal), names_sep = ".")