Accumulate over multiple columns horizontally with an R function
Description
This allows one to do rowwise operations, starting with an initial value
(acc). See pl$reduce() to do rowwise
operations without this initial value.
Usage
pl$fold(acc, lambda, exprs)
Arguments
acc
|
an Expr or Into |
lambda
|
R function which takes two polars Series as input and return one. |
exprs
|
Expressions to aggregate over. May also be a wildcard expression. |
Value
An expression that will be applied rowwise
Examples
library("polars")
df = as_polars_df(mtcars)
# Make the row-wise sum of all columns
df$with_columns(
pl$fold(
acc = pl$lit(0),
lambda = \(acc, x) acc + x,
exprs = pl$col("*")
)$alias("mpg_drat_sum_folded")
)
#> shape: (32, 12)
#> ┌──────┬─────┬───────┬───────┬───┬─────┬──────┬──────┬─────────────────────┐
#> │ mpg ┆ cyl ┆ disp ┆ hp ┆ … ┆ am ┆ gear ┆ carb ┆ mpg_drat_sum_folded │
#> │ --- ┆ --- ┆ --- ┆ --- ┆ ┆ --- ┆ --- ┆ --- ┆ --- │
#> │ f64 ┆ f64 ┆ f64 ┆ f64 ┆ ┆ f64 ┆ f64 ┆ f64 ┆ f64 │
#> ╞══════╪═════╪═══════╪═══════╪═══╪═════╪══════╪══════╪═════════════════════╡
#> │ 21.0 ┆ 6.0 ┆ 160.0 ┆ 110.0 ┆ … ┆ 1.0 ┆ 4.0 ┆ 4.0 ┆ 328.98 │
#> │ 21.0 ┆ 6.0 ┆ 160.0 ┆ 110.0 ┆ … ┆ 1.0 ┆ 4.0 ┆ 4.0 ┆ 329.795 │
#> │ 22.8 ┆ 4.0 ┆ 108.0 ┆ 93.0 ┆ … ┆ 1.0 ┆ 4.0 ┆ 1.0 ┆ 259.58 │
#> │ 21.4 ┆ 6.0 ┆ 258.0 ┆ 110.0 ┆ … ┆ 0.0 ┆ 3.0 ┆ 1.0 ┆ 426.135 │
#> │ 18.7 ┆ 8.0 ┆ 360.0 ┆ 175.0 ┆ … ┆ 0.0 ┆ 3.0 ┆ 2.0 ┆ 590.31 │
#> │ … ┆ … ┆ … ┆ … ┆ … ┆ … ┆ … ┆ … ┆ … │
#> │ 30.4 ┆ 4.0 ┆ 95.1 ┆ 113.0 ┆ … ┆ 1.0 ┆ 5.0 ┆ 2.0 ┆ 273.683 │
#> │ 15.8 ┆ 8.0 ┆ 351.0 ┆ 264.0 ┆ … ┆ 1.0 ┆ 5.0 ┆ 4.0 ┆ 670.69 │
#> │ 19.7 ┆ 6.0 ┆ 145.0 ┆ 175.0 ┆ … ┆ 1.0 ┆ 5.0 ┆ 6.0 ┆ 379.59 │
#> │ 15.0 ┆ 8.0 ┆ 301.0 ┆ 335.0 ┆ … ┆ 1.0 ┆ 5.0 ┆ 8.0 ┆ 694.71 │
#> │ 21.4 ┆ 4.0 ┆ 121.0 ┆ 109.0 ┆ … ┆ 1.0 ┆ 4.0 ┆ 2.0 ┆ 288.89 │
#> └──────┴─────┴───────┴───────┴───┴─────┴──────┴──────┴─────────────────────┘