@antv/g2
Version:
the Grammar of Graphics in Javascript
64 lines • 2.18 kB
JavaScript
// @ts-ignore medianIndex exist in d3-array@3.2.0, but @types/d3-array Expired.
import { maxIndex, minIndex, medianIndex } from '@antv/vendor/d3-array';
import { createGroups } from './utils/order';
import { columnOf } from './utils/helper';
import { lttb } from './utils/lttb';
function normalizeSample(strategy) {
if (typeof strategy === 'function')
return strategy;
if (strategy === 'lttb')
return lttb;
const strategies = {
first: (f) => [f[0]],
last: (f) => [f[f.length - 1]],
min: (f, X, Y) => [
f[minIndex(f, (i) => Y[i])],
],
max: (f, X, Y) => [
f[maxIndex(f, (i) => Y[i])],
],
median: (f, X, Y) => [
f[medianIndex(f, (i) => Y[i])],
],
};
const sampleFunction = strategies[strategy] || strategies.median;
return (I, X, Y, thresholds) => {
// Sepreate group to frames, then sample each frame.
// Keep more data as possible.
const frameSize = Math.max(1, Math.floor(I.length / thresholds));
const frames = getFrames(I, frameSize);
return frames.flatMap((frame) => sampleFunction(frame, X, Y));
};
}
/**
* Split the array into frame with each frameSize.
*/
function getFrames(I, frameSize) {
const size = I.length;
const frames = [];
let i = 0;
while (i < size) {
frames.push(I.slice(i, (i += frameSize)));
}
return frames;
}
/**
* The sample transform groups marks with specified groupBy fields, and
* sample data for each group when data.length >= threshold(default = 2000).
*/
export const Sample = (options = {}) => {
const { strategy = 'median', thresholds = 2000, groupBy = ['series', 'color'], } = options;
const sampleFunction = normalizeSample(strategy);
return (I, mark) => {
const { encode } = mark;
const groups = createGroups(groupBy, I, mark);
const [X] = columnOf(encode, 'x');
const [Y] = columnOf(encode, 'y');
return [
groups.flatMap((g) => sampleFunction(g, X, Y, thresholds)),
mark,
];
};
};
Sample.props = {};
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