Concat the arrays in a Series dtype List in linear time.

Description

Folds the expressions from left to right, keeping the first non-null value.

Usage

pl$concat_list(exprs)

Arguments

exprs list of Into, strings interpreted as column names

Value

Expr

Examples

library(polars)

# Create lagged columns and collect them into a list. This mimics a rolling window.
df = pl$DataFrame(A = c(1, 2, 9, 2, 13))
df$with_columns(lapply(
  0:2,
  \(i) pl$col("A")$shift(i)$alias(paste0("A_lag_", i))
))$select(
  pl$concat_list(lapply(2:0, \(i) pl$col(paste0("A_lag_", i))))$alias(
    "A_rolling"
  )
)

#> shape: (5, 1)
#> ┌───────────────────┐
#> │ A_rolling         │
#> │ ---               │
#> │ list[f64]         │
#> ╞═══════════════════╡
#> │ [null, null, 1.0] │
#> │ [null, 1.0, 2.0]  │
#> │ [1.0, 2.0, 9.0]   │
#> │ [2.0, 9.0, 2.0]   │
#> │ [9.0, 2.0, 13.0]  │
#> └───────────────────┘

# concat Expr a Series and an R obejct
pl$concat_list(list(
  pl$lit(1:5),
  as_polars_series(5:1),
  rep(0L, 5)
))$alias("alice")$to_series()

#> polars Series: shape: (5,)
#> Series: 'alice' [list[i32]]
#> [
#>  [1, 5, 0]
#>  [2, 4, 0]
#>  [3, 3, 0]
#>  [4, 2, 0]
#>  [5, 1, 0]
#> ]