Locate First Predicate Match — locate_by

Scans accumulated monoid values and returns the first element where predicate becomes TRUE, without rebuilding split trees.

Usage

locate_by_predicate(
  t,
  predicate,
  monoid_name,
  accumulator = NULL,
  include_metadata = FALSE
)

Arguments

t: A flexseq (or subclass).
predicate: Function applied to accumulated monoid values.
monoid_name: Name of the monoid used for scanning.
accumulator: Optional starting accumulator value.
include_metadata: Logical; include scan metadata.

Value

If include_metadata = FALSE, a list with:

found: logical flag.
value: matched element when found, otherwise NULL.

If include_metadata = TRUE, adds metadata with:

left_measure
hit_measure
right_measure
index

Details

This is the read-only analogue of split_around_by_predicate().

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

value is the matched leaf entry for the input structure:

flexseq: stored user element.
ordered_sequence: list(value, key).
priority_queue: list(value, priority).
interval_index: list(value, start, end).

Examples

x <- flexseq("a", "b", "c", "d")
size_monoid <- measure_monoid(`+`, 0L, function(e) 1L)
x2 <- add_monoids(x, list(size = size_monoid))

locate_by_predicate(x2, function(v) v >= 3L, "size")
#> $found
#> [1] TRUE
#> 
#> $value
#> [1] "c"
#> 
locate_by_predicate(x2, function(v) v >= 3L, "size", include_metadata = TRUE)
#> $found
#> [1] TRUE
#> 
#> $value
#> [1] "c"
#> 
#> $metadata
#> $metadata$left_measure
#> [1] 2
#> 
#> $metadata$hit_measure
#> [1] 3
#> 
#> $metadata$right_measure
#> [1] 1
#> 
#> $metadata$index
#> [1] 3
#> 
#>