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e7227f51b7
* Added JSDoc for internal types and constants e.g. Unts and earthRadius. Minimal other changes to bring JSDoc types into line with code types. Added GeoJsonProperties to documentation.yml for type linking. * Generated README.md files based on updated source that now includes JSDoc for internal types and constants e.g. Units. Also synced up some out of data JSDoc types with what is in the code. * Switched the structure of documentation.yml to be more traditionally nested. We'll use this new structure from the turf-www repo to generate the website documentation in a more robust manner. * For some reason leaving this function documented as the default (geojsonRbush) causes @turf/turf last-checks to fail. Specifically defining it as rbush like it used to be, except with the @function tag rather than @name.
55 lines
1.7 KiB
TypeScript
55 lines
1.7 KiB
TypeScript
// http://stackoverflow.com/questions/11935175/sampling-a-random-subset-from-an-array
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import { Feature, FeatureCollection, Geometry, GeometryObject } from "geojson";
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import { featureCollection } from "@turf/helpers";
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/**
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* Takes a {@link FeatureCollection} and returns a FeatureCollection with given number of {@link Feature|features} at random.
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*
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* @function
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* @param {FeatureCollection} featurecollection set of input features
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* @param {number} num number of features to select
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* @returns {FeatureCollection} a FeatureCollection with `n` features
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* @example
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* var points = turf.randomPoint(100, {bbox: [-80, 30, -60, 60]});
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*
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* var sample = turf.sample(points, 5);
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*
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* //addToMap
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* var addToMap = [points, sample]
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* turf.featureEach(sample, function (currentFeature) {
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* currentFeature.properties['marker-size'] = 'large';
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* currentFeature.properties['marker-color'] = '#000';
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* });
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*/
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function sample<T extends GeometryObject>(
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fc: FeatureCollection<T>,
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num: number
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): FeatureCollection<T> {
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if (!fc) throw new Error("fc is required");
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if (num === null || num === undefined) throw new Error("num is required");
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if (typeof num !== "number") throw new Error("num must be a number");
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var outFC = featureCollection(getRandomSubarray(fc.features, num));
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return outFC;
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}
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function getRandomSubarray<T extends Geometry>(
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arr: Feature<T>[],
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size: number
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) {
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var shuffled = arr.slice(0),
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i = arr.length,
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min = i - size,
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temp,
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index;
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while (i-- > min) {
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index = Math.floor((i + 1) * Math.random());
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temp = shuffled[index];
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shuffled[index] = shuffled[i];
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shuffled[i] = temp;
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}
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return shuffled.slice(min);
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}
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export { sample };
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export default sample;
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