polars.Expr.rle_id#

Expr.rle_id() → Self[source]#

Get a distinct integer ID for each run of identical values.

The ID starts at 0 and increases by one each time the value of the column changes.

Returns:

Expr: Expression of data type UInt32.

See also

rle

Notes

This functionality is especially useful for defining a new group for every time a column’s value changes, rather than for every distinct value of that column.

Examples

>>> df = pl.DataFrame(
...     {
...         "a": [1, 2, 1, 1, 1],
...         "b": ["x", "x", None, "y", "y"],
...     }
... )
>>> df.with_columns(
...     rle_id_a=pl.col("a").rle_id(),
...     rle_id_ab=pl.struct("a", "b").rle_id(),
... )
shape: (5, 4)
┌─────┬──────┬──────────┬───────────┐
│ a   ┆ b    ┆ rle_id_a ┆ rle_id_ab │
│ --- ┆ ---  ┆ ---      ┆ ---       │
│ i64 ┆ str  ┆ u32      ┆ u32       │
╞═════╪══════╪══════════╪═══════════╡
│ 1   ┆ x    ┆ 0        ┆ 0         │
│ 2   ┆ x    ┆ 1        ┆ 1         │
│ 1   ┆ null ┆ 2        ┆ 2         │
│ 1   ┆ y    ┆ 2        ┆ 3         │
│ 1   ┆ y    ┆ 2        ┆ 3         │
└─────┴──────┴──────────┴───────────┘