Split into Left and Right Parts

Splits at the first point where predicate becomes TRUE while scanning the sequence.

Usage

split_by_predicate(x, predicate, monoid_name)

Arguments

x

A flexseq (or subclass).

predicate

Function applied to accumulated monoid values.

monoid_name

Name of the monoid used for scanning.

Value

A list with fields:

• left: elements before the split point.

• right: elements from the split point onward.

Details

This is the two-way variant of split_around_by_predicate().

As with split_around_by_predicate(), a common setup is a custom monoid created with measure_monoid() and attached via add_monoids().

left and right preserve subclass when the input is a subclass of flexseq.

Examples

x <- flexseq("a", "b", "c", "d")
size_monoid <- measure_monoid(`+`, 0L, function(e) 1L)
x2 <- add_monoids(x, list(size = size_monoid))
split_by_predicate(x2, function(v) v >= 3L, "size")
#> $left
#> Unnamed flexseq with 2 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "a"
#> 
#> [[2]]
#> [1] "b"
#> 
#> 
#> $right
#> Unnamed flexseq with 2 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "c"
#> 
#> [[2]]
#> [1] "d"
#> 
#> 

# Split at the first element
split_by_predicate(x2, function(v) v >= 1L, "size")
#> $left
#> Unnamed flexseq with 0 elements.
#> 
#> $right
#> Unnamed flexseq with 4 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "a"
#> 
#> [[2]]
#> [1] "b"
#> 
#> [[3]]
#> [1] "c"
#> 
#> [[4]]
#> [1] "d"
#> 
#>