Start a group by operation

Description

Usage

<LazyFrame>$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.

Value

A lazy groupby

Examples

library("polars")

# Group by one column and call agg() to compute the grouped sum of another
# column.
lf <- pl$LazyFrame(
  a = c("a", "b", "a", "b", "c"),
  b = c(1, 2, 1, 3, 3),
  c = c(5, 4, 3, 2, 1)
)
lf$group_by("a")$agg(pl$col("b")$sum())$collect()

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

# Set .maintain_order = TRUE to ensure the order of the groups is consistent
# with the input.
lf$group_by("a", .maintain_order = TRUE)$agg(pl$col("b")$sum())$collect()

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

# Group by multiple columns by passing a vector of column names.
lf$group_by(c("a", "b"))$agg(pl$col("c")$max())$collect()

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

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

#> shape: (4, 3)
#> ┌─────┬─────┬─────┐
#> │ a   ┆ b   ┆ c   │
#> │ --- ┆ --- ┆ --- │
#> │ str ┆ f64 ┆ f64 │
#> ╞═════╪═════╪═════╡
#> │ b   ┆ 1.5 ┆ 2.0 │
#> │ c   ┆ 1.5 ┆ 1.0 │
#> │ b   ┆ 1.0 ┆ 4.0 │
#> │ a   ┆ 0.5 ┆ 4.0 │
#> └─────┴─────┴─────┘