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// Copyright 2018-2025 the Deno authors. MIT license.
// This module is browser compatible.
/** Options for {@linkcode slidingWindows}. */
export interface SlidingWindowsOptions {
/**
* If step is set, each window will start that many elements after the last
* window's start.
*
* @default {1}
*/
step?: number;
/**
* If partial is set, windows will be generated for the last elements of the
* collection, resulting in some undefined values if size is greater than 1.
*
* @default {false}
*/
partial?: boolean;
}
/**
* Generates sliding views of the given iterable of the given size and returns an
* array containing all of them.
*
* @experimental **UNSTABLE**: New API, yet to be vetted.
*
* If step is set, each window will start that many elements after the last
* window's start. (Default: 1)
*
* If partial is set, windows will be generated for the last elements of the
* collection, resulting in some undefined values if size is greater than 1.
*
* @typeParam T The type of the array elements.
*
* @param iterable The iterable to generate sliding windows from.
* @param size The size of the sliding windows.
* @param options The options for generating sliding windows.
*
* @returns An array containing all sliding windows of the given size.
*
* @example Usage
* ```ts
* import { slidingWindows } from "@std/collections/unstable-sliding-windows";
* import { assertEquals } from "@std/assert";
* const numbers = [1, 2, 3, 4, 5];
*
* const windows = slidingWindows(numbers, 3);
* assertEquals(windows, [
* [1, 2, 3],
* [2, 3, 4],
* [3, 4, 5],
* ]);
*
* const windowsWithStep = slidingWindows(numbers, 3, { step: 2 });
* assertEquals(windowsWithStep, [
* [1, 2, 3],
* [3, 4, 5],
* ]);
*
* const windowsWithPartial = slidingWindows(numbers, 3, { partial: true });
* assertEquals(windowsWithPartial, [
* [1, 2, 3],
* [2, 3, 4],
* [3, 4, 5],
* [4, 5],
* [5],
* ]);
* ```
*/
export function slidingWindows<T>(
iterable: Iterable<T>,
size: number,
options: SlidingWindowsOptions = {},
): T[][] {
const { step = 1, partial = false } = options;
if (!Number.isInteger(size) || size <= 0) {
throw new RangeError(
`Cannot create sliding windows: size must be a positive integer, current value is ${size}`,
);
}
if (!Number.isInteger(step) || step <= 0) {
throw new RangeError(
`Cannot create sliding windows: step must be a positive integer, current value is ${step}`,
);
}
const array = Array.isArray(iterable) ? iterable : Array.from(iterable);
const len = array.length;
const result: T[][] = [];
for (let i = 0; i <= len; i += step) {
let last = i + size;
if (last > len) {
last = len;
}
const window: T[] = array.slice(i, last);
if ((partial && window.length) || window.length === size) {
result.push(window);
}
}
return result;
}
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