Function filter

Standard Array.filter logic for the iterable, extended with iteration state.

In the example below, we are able to use a type guard to filter out all the nullable values.

import {pipe, filter} from 'iter-ops';

const i = pipe(
    [1, null, "foo"],
    filter((value): value is NonNullable<typeof value> => value != null)
);
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Note: The asynchronous version of this function cannot make use of type guards.
Give a :+1: to the Asynchronous Type Guards issue if you want support for this.

See

• Array.filter

Standard Array.filter logic for the iterable, extended with iteration state + async.

In the example below, we take advantage of the IterationState, to detect and remove repeated values (do not confuse with distinct, which removes all duplicates).

import {pipe, filter} from 'iter-ops';

const i = pipe(
    iterable,
    filter((value, index, state) => {
        if(value === state.previousValue) {
            return false;
        }
        state.previousValue = value;
        return true;
    })
);
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Note that the predicate can only return a Promise inside an asynchronous pipeline, or else the Promise will be treated as a truthy value.

See

• Array.filter