polars.fold#

polars.fold(acc: IntoExpr, f: Callable[[Series, Series], Series], exprs: Sequence[Expr | str] | Expr) Expr[source]#

Accumulate over multiple columns horizontally/ row wise with a left fold.

Parameters:
acc

Accumulator Expression. This is the value that will be initialized when the fold starts. For a sum this could for instance be lit(0).

f

Function to apply over the accumulator and the value. Fn(acc, value) -> new_value

exprs

Expressions to aggregate over. May also be a wildcard expression.

Notes

If you simply want the first encountered expression as accumulator, consider using reduce.