polars.Expr.cum_count#

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

Return the cumulative count of the non-null values in the column.

Parameters:

reverse: Reverse the operation.

Examples

>>> df = pl.DataFrame({"a": ["x", "k", None, "d"]})
>>> 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 │
│ ---  ┆ ---       ┆ ---               │
│ str  ┆ u32       ┆ u32               │
╞══════╪═══════════╪═══════════════════╡
│ x    ┆ 1         ┆ 3                 │
│ k    ┆ 2         ┆ 2                 │
│ null ┆ 2         ┆ 1                 │
│ d    ┆ 3         ┆ 1                 │
└──────┴───────────┴───────────────────┘