collectors

Collectors are functions that return a new object instance of type TerminalStage.

Example usage

import { LazyPipeline } from 'lazy-pipeline';
import { allMatch } from 'lazy-pipeline/collectors';
import { limit } from 'lazy-pipeline/operators';

const source = [2, 4, 6, 8, 10];

const result = LazyPipeline.from(source)
  .add(
    /*
     * Only take the first 3 elements.
     */
    limit(3)
  )
  .collect(
    /**
     * `allMatch() collector returns whether all remaining elements in this pipeline are even numbers.
     */
    allMatch(e => e % 2 === 0)
  );

console.log(result); // Outputs `true`.

Built-in collectors

Collector	Description
allMatch	Return a terminal stage that evaluates whether all elements in the pipeline match the provided predicate.
anyMatch	Return a terminal stage that evaluates whether at least one element in the pipeline matches the provided predicate.
average	Return a terminal stage that calculates the average of all numeric elements in the pipeline. This collector throws an error if at least one element is not numeric.
count	Return a terminal stage that calculates the total number of elements in the pipeline.
findFirst	Return a short-circuiting terminal stage that retrieves the very first element encountered in the pipeline. The pipeline will terminate as soon as an element is found due to its short-circuiting nature, otherwise, undefined is returned.
findLast	Return a terminal stage that finds and retrieves the very last element in the pipeline. If no such element exists, undefined is returned.
forEach	Return a terminal stage that executes the given action on each pipeline element.
groupBy	Return a terminal stage that groups pipeline elements by the keys returned by keyExtractor argument. Elements that return the same key will be grouped together in an array used as the value in the mapping. Optionally, each grouped element can be transformed by providing a second argument.
join	Return a terminal stage that concatenates the input elements, separated by the specified delimiter, in encounter order.
max	Return a terminal stage that finds the max element in the pipeline. By default, if no comparator function is provided, it assumes every element to be numeric, if at least one element is not numeric, then it will throw an error. If a comparator function is provided, it will use the returned value of the comparator as the max.
min	Return a terminal stage that finds the min element in the pipeline. By default, if no comparator function is provided, it assumes every element to be numeric, if at least one element is not numeric, then it will throw an error. If a comparator function is provided, it will use the returned value of the comparator as the min.
noneMatch	Return a terminal stage that checks whether no elements in this pipeline match the provided predicate.
reduce	Return a terminal stage that performs a reduction of the received pipeline elements using the provided reducer function, optionally accepting an initial value as the second argument. The reducer function accepts 2 arguments, the first argument is the accumulator value that will be returned when the reduction is complete, the second argument is the next pipeline element to reduce into the accumulator. This collector's behavior is similar to that of Array.prototype.reduce.
sum	Return a terminal stage that calculates the sum of all elements in this pipeline. It assumes that every element is numeric, otherwise, it will throw an error when at least one element is not numeric.
toArray	Return a terminal stage that collects all elements in the pipeline into an array.
toMap	Return a terminal stage that puts each element into a map whose keys are extracted from keyExtractor argument. Optionally, each element can be transformed by providing a second argument before being stored in the resulting map.
toObject	Return a terminal stage that puts each element into a plain object whose keys are extracted from keyExtractor argument. Optionally, each element can be transformed by providing a second argument before being stored in the resulting object.