polars.Expr.cum_count#

Expr.cum_count(*, reverse: bool = False) → Self[source]#

Get an array with the cumulative count computed at every element.

Counting from 0 to len

Parameters:

reverse: Reverse the operation.

Examples

>>> df = pl.DataFrame({"a": [1, 2, 3, 4]})
>>> df.with_columns(
...     pl.col("a").cum_count().alias("cum_count"),
...     pl.col("a").cum_count(reverse=True).alias("cum_count_reverse"),
... )
shape: (4, 3)
┌─────┬───────────┬───────────────────┐
│ a   ┆ cum_count ┆ cum_count_reverse │
│ --- ┆ ---       ┆ ---               │
│ i64 ┆ u32       ┆ u32               │
╞═════╪═══════════╪═══════════════════╡
│ 1   ┆ 0         ┆ 3                 │
│ 2   ┆ 1         ┆ 2                 │
│ 3   ┆ 2         ┆ 1                 │
│ 4   ┆ 3         ┆ 0                 │
└─────┴───────────┴───────────────────┘