Filter the expression based on one or more predicate expressions

Description

Elements where the filter does not evaluate to TRUE are discarded, including nulls. This is mostly useful in an aggregation context. If you want to filter on a DataFrame level, use DataFrame$filter() or LazyFrame$filter().

Usage

<Expr>$filter(...)

Arguments

…	\<dynamic-dots\> Expression(s) that evaluate to a boolean Series.

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(
  group_col = c("g1", "g1", "g2"),
  b = c(1, 2, 3)
)
df

#> shape: (3, 2)
#> ┌───────────┬─────┐
#> │ group_col ┆ b   │
#> │ ---       ┆ --- │
#> │ str       ┆ f64 │
#> ╞═══════════╪═════╡
#> │ g1        ┆ 1.0 │
#> │ g1        ┆ 2.0 │
#> │ g2        ┆ 3.0 │
#> └───────────┴─────┘

df$group_by("group_col")$agg(
  lt = pl$col("b")$filter(pl$col("b") < 2),
  gte = pl$col("b")$filter(pl$col("b") >= 2)
)

#> shape: (2, 3)
#> ┌───────────┬───────────┬───────────┐
#> │ group_col ┆ lt        ┆ gte       │
#> │ ---       ┆ ---       ┆ ---       │
#> │ str       ┆ list[f64] ┆ list[f64] │
#> ╞═══════════╪═══════════╪═══════════╡
#> │ g1        ┆ [1.0]     ┆ [2.0]     │
#> │ g2        ┆ []        ┆ [3.0]     │
#> └───────────┴───────────┴───────────┘