polars.Expr.list.count_matches

Expr.list.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": [[0], [1], [1, 2, 3, 2], [1, 2, 1], [4, 4]]})
>>> df.with_columns(number_of_twos=pl.col("a").list.count_matches(2))
shape: (5, 2)
┌─────────────┬────────────────┐
│ a           ┆ number_of_twos │
│ ---         ┆ ---            │
│ list[i64]   ┆ u32            │
╞═════════════╪════════════════╡
│ [0]         ┆ 0              │
│ [1]         ┆ 0              │
│ [1, 2, … 2] ┆ 2              │
│ [1, 2, 1]   ┆ 1              │
│ [4, 4]      ┆ 0              │
└─────────────┴────────────────┘