Group a DataFrame

Description

Group a DataFrame

Usage

<DataFrame>$group_by(..., .maintain_order = FALSE)

Arguments

…	\<dynamic-dots\> Column(s) to group by. Accepts expression input. Strings are parsed as column names.
.maintain_order	Ensure that the order of the groups is consistent with the input data. This is slower than a default group by. Setting this to TRUE blocks the possibility to run on the streaming engine.

Details

Within each group, the order of the rows is always preserved, regardless of the maintain_order argument.

Value

An object of class polars_group_by

See Also

• \$partition_by()

Examples

library("polars")

df <- pl$DataFrame(
  a = c("a", "b", "a", "b", "c"),
  b = c(1, 2, 1, 3, 3),
  c = c(5, 4, 3, 2, 1)
)

df$group_by("a")$agg(pl$col("b")$sum())

#> shape: (3, 2)
#> ┌─────┬─────┐
#> │ a   ┆ b   │
#> │ --- ┆ --- │
#> │ str ┆ f64 │
#> ╞═════╪═════╡
#> │ c   ┆ 3.0 │
#> │ a   ┆ 2.0 │
#> │ b   ┆ 5.0 │
#> └─────┴─────┘

# Set `maintain_order = TRUE` to ensure the order of the groups is
# consistent with the input.
df$group_by("a", .maintain_order = TRUE)$agg(pl$col("c"))

#> shape: (3, 2)
#> ┌─────┬────────────┐
#> │ a   ┆ c          │
#> │ --- ┆ ---        │
#> │ str ┆ list[f64]  │
#> ╞═════╪════════════╡
#> │ a   ┆ [5.0, 3.0] │
#> │ b   ┆ [4.0, 2.0] │
#> │ c   ┆ [1.0]      │
#> └─────┴────────────┘

# Group by multiple columns by passing a list of column names.
df$group_by(c("a", "b"))$agg(pl$max("c"))

#> shape: (4, 3)
#> ┌─────┬─────┬─────┐
#> │ a   ┆ b   ┆ c   │
#> │ --- ┆ --- ┆ --- │
#> │ str ┆ f64 ┆ f64 │
#> ╞═════╪═════╪═════╡
#> │ c   ┆ 3.0 ┆ 1.0 │
#> │ b   ┆ 3.0 ┆ 2.0 │
#> │ a   ┆ 1.0 ┆ 5.0 │
#> │ b   ┆ 2.0 ┆ 4.0 │
#> └─────┴─────┴─────┘

# Or pass some arguments to group by multiple columns in the same way.
# Expressions are also accepted.
df$group_by("a", pl$col("b") %/% 2)$agg(
  pl$col("c")$mean()
)

#> shape: (3, 3)
#> ┌─────┬─────┬─────┐
#> │ a   ┆ b   ┆ c   │
#> │ --- ┆ --- ┆ --- │
#> │ str ┆ f64 ┆ f64 │
#> ╞═════╪═════╪═════╡
#> │ c   ┆ 1.0 ┆ 1.0 │
#> │ a   ┆ 0.0 ┆ 4.0 │
#> │ b   ┆ 1.0 ┆ 3.0 │
#> └─────┴─────┴─────┘

# The columns will be renamed to the argument names.
df$group_by(d = "a", e = pl$col("b") %/% 2)$agg(
  pl$col("c")$mean()
)

#> shape: (3, 3)
#> ┌─────┬─────┬─────┐
#> │ d   ┆ e   ┆ c   │
#> │ --- ┆ --- ┆ --- │
#> │ str ┆ f64 ┆ f64 │
#> ╞═════╪═════╪═════╡
#> │ c   ┆ 1.0 ┆ 1.0 │
#> │ a   ┆ 0.0 ┆ 4.0 │
#> │ b   ┆ 1.0 ┆ 3.0 │
#> └─────┴─────┴─────┘