polars.Expr.arr.count_matches

Expr.arr.count_matches(element: IntoExpr) → Expr

Count how often the value produced by element occurs.

Parameters:

element

An expression that produces a single value

Examples

>>> df = pl.DataFrame(
...     {"a": [[1, 2], [1, 1], [2, 2]]}, schema={"a": pl.Array(pl.Int64, 2)}
... )
>>> df.with_columns(number_of_twos=pl.col("a").arr.count_matches(2))
shape: (3, 2)
┌───────────────┬────────────────┐
│ a             ┆ number_of_twos │
│ ---           ┆ ---            │
│ array[i64, 2] ┆ u32            │
╞═══════════════╪════════════════╡
│ [1, 2]        ┆ 1              │
│ [1, 1]        ┆ 0              │
│ [2, 2]        ┆ 2              │
└───────────────┴────────────────┘