Sparse tibbles with constant columns stored as one value

[vspinu]

This is related to r-lib/vctrs#27 and #196 but I feel that a separate discussion is warranted here.

I would like to see a very simple sparse tibble where constant columns could be stored as a single value. So a tibble like this:

> tibble(a = 1:3, b = 1)
# A tibble: 3 x 2
      a     b
  <int> <dbl>
1     1     1
2     2     1
3     3     1
> 

is internally stored as:

> list(a = 1:3, b = 1)
$a
[1] 1 2 3

$b
[1] 1

This way you could store attributes along the data itself without extra space requirements and completely avoid dealing with R attributes. If such an attribute is an atomic singleton most vectorized operations should automatically propagate due to R's recycling rules and behave as if it's a proper column.

For what it's worth, I would need this for a more lightweight and more generic version of periods than what's currently implemented in lubridate.

[hadley]

I think this is out of scope for tibble - I think it will be a lot of work to implement (and it can't work for any C functions that don't call as.data.frame()), so it's worth starting incubating somewhere else. If the incubation is successful we could consider incorporating into tibble.

[krlmlr]

How much of this would ALTREP support out of the box?

[github-actions]

This old thread has been automatically locked. If you think you have found something related to this, please open a new issue and link to this old issue if necessary.