polars.Expr.min_by

Expr.min_by(by: IntoExpr) → Expr

Get minimum value, ordered by another expression.

If the by expression has multiple values equal to the minimum it is not defined which value will be chosen.

Warning

This functionality is considered unstable. It may be changed at any point without it being considered a breaking change.

Parameters:

by

Column used to determine the smallest element. Accepts expression input. Strings are parsed as column names.

Examples

>>> df = pl.DataFrame({"a": [-1.0, float("nan"), 1.0], "b": ["x", "y", "z"]})
>>> df.select(pl.col("b").min_by("a"))
shape: (1, 1)
┌─────┐
│ b   │
│ --- │
│ str │
╞═════╡
│ x   │
└─────┘