Return the cumulative sum computed at every element.

Description

Usage

<Expr>$cum_sum(..., reverse = FALSE)

Arguments

… These dots are for future extensions and must be empty.

reverse If TRUE, start with the total sum of elements and substract each row one by one.

Details

The Dtypes Int8, UInt8, Int16 and UInt16 are cast to Int64 before summing to prevent overflow issues.

Value

A polars expression

Examples

library("polars")

pl$DataFrame(a = 1:4)$with_columns(
  cum_sum = pl$col("a")$cum_sum(),
  cum_sum_reversed = pl$col("a")$cum_sum(reverse = TRUE)
)

#> shape: (4, 3)
#> ┌─────┬─────────┬──────────────────┐
#> │ a   ┆ cum_sum ┆ cum_sum_reversed │
#> │ --- ┆ ---     ┆ ---              │
#> │ i32 ┆ i32     ┆ i32              │
#> ╞═════╪═════════╪══════════════════╡
#> │ 1   ┆ 1       ┆ 10               │
#> │ 2   ┆ 3       ┆ 9                │
#> │ 3   ┆ 6       ┆ 7                │
#> │ 4   ┆ 10      ┆ 4                │
#> └─────┴─────────┴──────────────────┘