Return the cumulative count of the non-null values in the column

Description

Usage

<Expr>$cumulative_eval(expr, ..., min_periods = 1, parallel = FALSE)

Arguments

expr Expression to evaluate.

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

min_periods Number of valid values (i.e. length - null_count) there should be in the window before the expression is evaluated.

parallel Run in parallel. Don’t do this in a group by or another operation that already has much parallelization.

Details

This can be really slow as it can have O(n^2) complexity. Don’t use this for operations that visit all elements.

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(values = 1:5)
df$with_columns(
  pl$col("values")$cumulative_eval(
    pl$element()$first() - pl$element()$last()**2
  )
)

#> shape: (5, 1)
#> ┌────────┐
#> │ values │
#> │ ---    │
#> │ f64    │
#> ╞════════╡
#> │ 0.0    │
#> │ -3.0   │
#> │ -8.0   │
#> │ -15.0  │
#> │ -24.0  │
#> └────────┘