Tracking issue for missing methods in arr namespace

[deanm0000]

Description

arr seems to be missing the following methods that ought to work with fixed sizes.

• concat
• eval
• gather
• gather_every
• len (feat: Add len method to arr #21618)
• mean
• sample
• slice
• head
• tail

As an aside, I see that arr.unique already exists which creates the precedent that an arr operation can return a list whereas I excluded operations that can't necessarily return a fixed size.

[mcrumiller]

It looks like arr.concat is actually implemented already as the pl.concat_arr function, it's just not exposed to the array namespace.

import polars as pl

s1 = pl.Series([[1, 2], [3, 4]], dtype=pl.Array(pl.Int32, 2))
s2 = pl.Series([[5, 6], [7, 8]], dtype=pl.Array(pl.Int32, 2))
>>> pl.select(pl.concat_arr((s1, s2)))
# shape: (2, 1)
# ┌───────────────┐
# │               │
# │ ---           │
# │ array[i32, 4] │
# ╞═══════════════╡
# │ [1, 2, … 6]   │
# │ [3, 4, … 8]   │
# └───────────────┘

[coastalwhite]

If anyone were to go about implementing this. Please, go method by method and don't do all at once. The compute-kernels used by the .list might be able to be reused.

[DhruvBShetty]

I would like to take this issue

[teomac]

Hi @DhruvBShetty
I'm already working on it :)

[coastalwhite]

For slice, head and tail, we will want an as_array flag akin to was done #20941. This will force the length (and offset) to be constant which will allow to keep the Array datatype.

Otherwise, those should output as pl.List as there is no way of knowing the datatype of a head(arbitary_expr) before evaluating the expression (and even then, the expression might not contain a constant value).