polars.Expr.list.gather_every#

Expr.list.gather_every( n: int | IntoExprColumn, offset: int | IntoExprColumn = 0, ) → Expr[source]#

Take every n-th value start from offset in sublists.

Parameters:

n: Gather every n-th element.
offset: Starting index.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [[1, 2, 3, 4, 5], [6, 7, 8], [9, 10, 11, 12]],
...         "n": [2, 1, 3],
...         "offset": [0, 1, 0],
...     }
... )
>>> df.with_columns(
...     gather_every=pl.col("a").list.gather_every(
...         n=pl.col("n"), offset=pl.col("offset")
...     )
... )
shape: (3, 4)
┌───────────────┬─────┬────────┬──────────────┐
│ a             ┆ n   ┆ offset ┆ gather_every │
│ ---           ┆ --- ┆ ---    ┆ ---          │
│ list[i64]     ┆ i64 ┆ i64    ┆ list[i64]    │
╞═══════════════╪═════╪════════╪══════════════╡
│ [1, 2, … 5]   ┆ 2   ┆ 0      ┆ [1, 3, 5]    │
│ [6, 7, 8]     ┆ 1   ┆ 1      ┆ [7, 8]       │
│ [9, 10, … 12] ┆ 3   ┆ 0      ┆ [9, 12]      │
└───────────────┴─────┴────────┴──────────────┘