cellxgene/client/src/util/dataframe/summarize.js

/*
Private dataframe support functions

TODO / XXX: for scalar/continuous data, this uses a naive method
of computing quantiles.  Would be good to switch from sort to 
partition at some point.
*/

import quantile from "../quantile";
import { sortArray } from "../typedCrossfilter/sort";

// [ 0, 0.01, 0.02, ..., 1.0]
const centileNames = new Array(101).fill(0).map((v, idx) => idx / 100);

export function summarizeContinuous(col) {
  let min;
  let max;
  let nan = 0;
  let pinf = 0;
  let ninf = 0;
  let percentiles;
  if (col) {
    // -Inf < finite < Inf < NaN
    const sortedCol = sortArray(new col.constructor(col));

    // count non-finites, which are at each end of sorted data
    for (let i = sortedCol.length - 1; i >= 0; i -= 1) {
      if (!Number.isNaN(sortedCol[i])) {
        nan = sortedCol.length - i - 1;
        break;
      }
    }
    for (let i = 0, l = sortedCol.length; i < l; i += 1) {
      if (sortedCol[i] !== Number.NEGATIVE_INFINITY) {
        ninf = i;
        break;
      }
    }
    for (let i = sortedCol.length - nan - 1; i >= 0; i -= 1) {
      if (sortedCol[i] !== Number.POSITIVE_INFINITY) {
        pinf = sortedCol.length - i - nan - 1;
        break;
      }
    }

    // compute percentiles on finite data ONLY
    const sortedColFiniteOnly = sortedCol.slice(
      ninf,
      sortedCol.length - nan - pinf
    );
    percentiles = quantile(centileNames, sortedColFiniteOnly, true);
    min = percentiles[0];
    max = percentiles[100];
  }
  return {
    categorical: false,
    min,
    max,
    nan,
    pinf,
    ninf,
    percentiles
  };
}

export function summarizeCategorical(col) {
  const categoryCounts = new Map();
  if (col) {
    for (let r = 0, l = col.length; r < l; r += 1) {
      const val = col[r];
      let curCount = categoryCounts.get(val);
      if (curCount === undefined) curCount = 0;
      categoryCounts.set(val, curCount + 1);
    }
  }
  return {
    categorical: true,
    categories: [...categoryCounts.keys()],
    categoryCounts,
    numCategories: categoryCounts.size
  };
}