polars.cumsum#

polars.cumsum(column: str | Sequence[Expr | str] | Expr) → Expr[source]#

polars.cumsum(column: Series) → int | float

Cumulatively sum values in a column/Series, or horizontally across list of columns/expressions.

pl.cumsum(str) is syntactic sugar for:

>>> pl.col(str).cumsum()  

pl.cumsum(list) is syntactic sugar for:

>>> pl.cumfold(pl.lit(0), lambda x, y: x + y, list).alias(
...     "cumsum"
... )  

Parameters:

column

Column(s) to be used in aggregation. This can be:

a column name, or Series -> aggregate the sum value of that column/Series.
a List[Expr] -> aggregate the sum value horizontally across the Expr result.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, 2],
...         "b": [3, 4],
...         "c": [5, 6],
...     }
... )
>>> df
shape: (2, 3)
┌─────┬─────┬─────┐
│ a   ┆ b   ┆ c   │
│ --- ┆ --- ┆ --- │
│ i64 ┆ i64 ┆ i64 │
╞═════╪═════╪═════╡
│ 1   ┆ 3   ┆ 5   │
│ 2   ┆ 4   ┆ 6   │
└─────┴─────┴─────┘

Cumulatively sum a column by name:

>>> df.select(pl.cumsum("a"))
shape: (2, 1)
┌─────┐
│ a   │
│ --- │
│ i64 │
╞═════╡
│ 1   │
│ 3   │
└─────┘

Cumulatively sum a list of columns/expressions horizontally:

>>> df.with_columns(pl.cumsum(["a", "c"]))
shape: (2, 4)
┌─────┬─────┬─────┬───────────┐
│ a   ┆ b   ┆ c   ┆ cumsum    │
│ --- ┆ --- ┆ --- ┆ ---       │
│ i64 ┆ i64 ┆ i64 ┆ struct[2] │
╞═════╪═════╪═════╪═══════════╡
│ 1   ┆ 3   ┆ 5   ┆ {1,6}     │
│ 2   ┆ 4   ┆ 6   ┆ {2,8}     │
└─────┴─────┴─────┴───────────┘