grafana/public/app/plugins/panel/graph/histogram.ts

import TimeSeries from 'app/core/time_series2';
import { histogram } from 'd3';

/**
 * Convert series into array of series values.
 * @param data Array of series
 */
export function getSeriesValues(dataList: TimeSeries[]): number[] {
  const VALUE_INDEX = 0;
  const values = [];

  // Count histogam stats
  for (let i = 0; i < dataList.length; i++) {
    const series = dataList[i];
    const datapoints = series.datapoints;
    for (let j = 0; j < datapoints.length; j++) {
      if (datapoints[j][VALUE_INDEX] !== null) {
        values.push(datapoints[j][VALUE_INDEX]);
      }
    }
  }

  return values;
}

/**
 * Convert array of values into timeseries-like histogram:
 * [[val_1, count_1], [val_2, count_2], ..., [val_n, count_n]]
 * @param values
 * @param bucketSize
 */
export function convertValuesToHistogram(values: number[], bucketSize: number, min: number, max: number): any[] {
  const minBound = getBucketBound(min, bucketSize);
  const maxBound = getBucketBound(max, bucketSize);

  const histGenerator = histogram()
    .domain([minBound, maxBound])
    .thresholds(Math.round(max - min) / bucketSize);

  return histGenerator(values).map((bin) => {
    return [bin.x0, bin.length];
  });
}

/**
 * Convert series into array of histogram data.
 * @param data Array of series
 * @param bucketSize
 */
export function convertToHistogramData(
  data: any,
  bucketSize: number,
  hiddenSeries: any,
  min: number,
  max: number
): any[] {
  return data.map((series: any) => {
    const values = getSeriesValues([series]);
    series.histogram = true;
    if (!hiddenSeries[series.alias]) {
      const histogram = convertValuesToHistogram(values, bucketSize, min, max);
      series.data = histogram;
    } else {
      series.data = [];
    }
    return series;
  });
}

function getBucketBound(value: number, bucketSize: number): number {
  return Math.floor(value / bucketSize) * bucketSize;
}