1 | // Copyright (c) Jupyter Development Team.
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2 | // Distributed under the terms of the Modified BSD License.
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3 | /*-----------------------------------------------------------------------------
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4 | | Copyright (c) 2014-2017, PhosphorJS Contributors
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5 | |
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6 | | Distributed under the terms of the BSD 3-Clause License.
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7 | |
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8 | | The full license is in the file LICENSE, distributed with this software.
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9 | |----------------------------------------------------------------------------*/
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10 | import { IIterator, iter, IterableOrArrayLike } from './iter';
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11 |
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12 | /**
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13 | * Iterate over an iterable using a stepped increment.
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14 | *
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15 | * @param object - The iterable or array-like object of interest.
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16 | *
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17 | * @param step - The distance to step on each iteration. A value
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18 | * of less than `1` will behave the same as a value of `1`.
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19 | *
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20 | * @returns An iterator which traverses the iterable step-wise.
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21 | *
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22 | * #### Example
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23 | * ```typescript
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24 | * import { stride, toArray } from '@lumino/algorithm';
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25 | *
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26 | * let data = [1, 2, 3, 4, 5, 6];
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27 | *
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28 | * let stream = stride(data, 2);
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29 | *
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30 | * toArray(stream); // [1, 3, 5];
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31 | * ```
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32 | */
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33 | export function stride<T>(
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34 | object: IterableOrArrayLike<T>,
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35 | step: number
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36 | ): IIterator<T> {
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37 | return new StrideIterator<T>(iter(object), step);
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38 | }
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39 |
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40 | /**
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41 | * An iterator which traverses a source iterator step-wise.
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42 | */
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43 | export class StrideIterator<T> implements IIterator<T> {
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44 | /**
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45 | * Construct a new stride iterator.
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46 | *
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47 | * @param source - The iterator of values of interest.
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48 | *
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49 | * @param step - The distance to step on each iteration. A value
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50 | * of less than `1` will behave the same as a value of `1`.
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51 | */
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52 | constructor(source: IIterator<T>, step: number) {
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53 | this._source = source;
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54 | this._step = step;
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55 | }
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56 |
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57 | /**
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58 | * Get an iterator over the object's values.
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59 | *
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60 | * @returns An iterator which yields the object's values.
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61 | */
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62 | iter(): IIterator<T> {
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63 | return this;
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64 | }
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65 |
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66 | /**
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67 | * Create an independent clone of the iterator.
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68 | *
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69 | * @returns A new independent clone of the iterator.
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70 | */
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71 | clone(): IIterator<T> {
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72 | return new StrideIterator<T>(this._source.clone(), this._step);
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73 | }
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74 |
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75 | /**
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76 | * Get the next value from the iterator.
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77 | *
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78 | * @returns The next value from the iterator, or `undefined`.
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79 | */
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80 | next(): T | undefined {
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81 | let value = this._source.next();
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82 | for (let n = this._step - 1; n > 0; --n) {
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83 | this._source.next();
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84 | }
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85 | return value;
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86 | }
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87 |
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88 | private _source: IIterator<T>;
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89 | private _step: number;
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90 | }
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