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Filter Operators

filter​

Filter items emitted by the source Observable by only emitting those that satisfy a specified predicate.

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import { from, filter } from "@devicescript/observables"

const obs = from([0, 1, 2, 3, 1])

obs
    .pipe(filter(v => v > 1))
    .subscribe(v => console.log(v))

debounceTime​

Emits a notification from the source Observable only after a particular time span has passed without another source emission.

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The example below debounce a button down event to one every 5 seconds.

import { Button } from "@devicescript/core"
import { debounceTime } from "@devicescript/observables"

const button = new Button()

button.down
    .pipe(debounceTime(5000))
    .subscribe(() => console.log("click"))

throttleTime​

Emits a value from the source Observable, then ignores subsequent source values for duration milliseconds, then repeats this process.

output.svg

The example below debounce a button down event to one every 5 seconds.

import { Button } from "@devicescript/core"
import { throttleTime } from "@devicescript/observables"

const button = new Button()

button.down
    .pipe(throttleTime(1000))
    .subscribe(() => console.log("click"))

auditTime​

Ignores source values for duration milliseconds, then emits the most recent value from the source Observable, then repeats this process

auditTime is similar to throttleTime, but emits the last value from the silenced time window, instead of the first value.

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The example below debounce a button down event to one every 5 seconds.

import { Button } from "@devicescript/core"
import { auditTime } from "@devicescript/observables"

const button = new Button()

button.down
    .pipe(auditTime(1000))
    .subscribe(() => console.log("click"))

threshold​

Filters numerical data stream within change threshold.

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The example tracks the temperature returned

import { Temperature } from "@devicescript/core"
import { threshold } from "@devicescript/observables"

const thermometer = new Temperature()

thermometer.reading
    .pipe(threshold(2))
    .subscribe(t => console.log(t))

distinctUntilChanged​

Returns a result Observable that emits all values pushed by the source observable if they are distinct in comparison to the last value the result observable emitted.

This function can be used to create user-friendly transformer. For example, thershold is as follows:

export function threshold<T = number>(
    value: number,
    ...
): OperatorFunction<T, T> {
    return distinctUntilChanged<T, number>(
        (l, r) => Math.abs(l - r) < value,
        keySelector
    )
}

Transform operators​

map​

Applies a converter function to converts the observed value into a new value.

output.svg
import { from, map } from "@devicescript/observables"

const obs = from([1, 2, 3])

obs
    .pipe(map(v => v * v))
    .subscribe(v => console.log(v))

scan​

Applies an accumulator (or "reducer function") to each value from the source.

output.svg
import { from, scan } from "@devicescript/observables"

const obs = from([1, 2, 3])

obs.pipe(
    scan((p, c) => p + c, 0)
).subscribe(v => console.log(v))

Signal processing​

ewma​

Exponentially weighted moving average is a simple PIR filter with a gain parameter. The closer gain to 1 and the more closely the EWMA tracks the original time series.

import { Temperature } from "@devicescript/core"
import { ewma } from "@devicescript/observables"

const thermometer = new Temperature()

thermometer.reading
    .pipe(ewma(0.5))
    .subscribe(t => console.log(t))

rollingAverage​

A windowed rolling average filter.

import { Temperature } from "@devicescript/core"
import { rollingAverage } from "@devicescript/observables"