# All files / transforms histogram.ts

100% Statements 76/76
100% Branches 17/17
100% Functions 5/5
100% Lines 68/68

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     import {range, thresholdSturges} from 'd3-array'

    import {FILL, X_MIN, X_MAX, Y_MIN, Y_MAX, COUNT} from '../constants/columnKeys'
    import {createGroupIDColumn, getNominalColorScale} from './'
    import {newTable} from '../utils/newTable'
    import {extentOfExtents} from '../utils/extrema'
    import {resolveDomain} from '../utils/resolveDomain'
    import {Table, RectLayerSpec, HistogramPosition} from '../types'

    export const histogramTransform = (
      inputTable: Table,
      xColumnKey: string,
      xDomain: number[],
      colors: string[],
      fillColKeys: string[],
      binCount: number,
      position: HistogramPosition
    ): RectLayerSpec => {
      const [fillColumn, fillColumnMap] = createGroupIDColumn(
        inputTable,
        fillColKeys
      )

      const resolvedXDomain = resolveDomain(
        inputTable.getColumn(xColumnKey, 'number'),
        xDomain
      )

      const table = bin(
        inputTable.addColumn(FILL, 'system', 'number', fillColumn),
        xColumnKey,
        resolvedXDomain,
        binCount,
        position
      )

      const fillScale = getNominalColorScale(fillColumnMap, colors)

      const yDomain = extentOfExtents(
        table.getColumn(Y_MIN) as number[],
        table.getColumn(Y_MAX) as number[]
      )

      return {
        type: 'rect',
        inputTable,
        table,
        binDimension: 'x',
        xColumnKey,
        yColumnKey: COUNT,
        xDomain: resolvedXDomain,
        yDomain,
        xColumnType: inputTable.getColumnType(xColumnKey),
        yColumnType: 'number',
        scales: {fill: fillScale},
        columnGroupMaps: {fill: fillColumnMap},
      }
    }

    /*
      Compute the data of a histogram visualization.

      The column specified by the `xColName` will be divided into `binCount` evenly
      spaced bins, and the number of rows in each bin will be counted.

      If the `groupKeyCols` option is passed, rows in each bin are further grouped
      by the set of values for the `groupKeyCols` for the row.

      The returned result is a table where each row represents a bar in a
      (potentially stacked) histogram. For example, a histogram with two bins and
      two groups in each bin (four bars total) might have a table that looks like
      this:

          xMin | xMax | yMin | yMax | host | cpu
          --------------------------------------
             0 |   10 |    0 |   21 |  "a" |   1
             0 |   10 |   21 |   30 |  "b" |   1
            10 |   20 |    0 |    4 |  "a" |   1
            10 |   20 |    4 |    6 |  "b" |   1

      If `binCount` is not provided, a default value will be provided using
      [Sturges' formula][0].

      [0]: https://en.wikipedia.org/wiki/Histogram#Sturges'_formula
    */
    export const bin = (
      table: Table,
      xColKey: string,
      xDomain: number[],
      binCount: number,
      position: HistogramPosition
    ): Table => {
      const xColData = table.getColumn(xColKey, 'number')
      const xColType = table.getColumnType(xColKey) as 'number'
      const xOriginalColType = table.getOriginalColumnType(xColKey) as
        | 'double'
        | 'long'
        | 'unsignedLong'
      const groupColData = table.getColumn(FILL, 'number')

      if (!binCount) {
        binCount = thresholdSturges(xColData)
      }

      const bins = createBins(xDomain, binCount)

      // Count x values by bin and group
      for (let i = 0; i < xColData.length; i++) {
        const x = xColData[i]

        const shouldSkipPoint =
          x === undefined ||
          x === null ||
          isNaN(x) ||
          x < xDomain[0] ||
          x > xDomain[1]

        if (shouldSkipPoint) {
          continue
        }

        const xPercentage = (x - xDomain[0]) / (xDomain[1] - xDomain[0])

        let binIndex = Math.floor(xPercentage * binCount)

        if (binIndex === bins.length) {
          // Special case: the maximum value should be clamped to the last bin
          binIndex = bins.length - 1
        }

        const bin = bins[binIndex]
        const groupID = groupColData[i]

        if (!bin.values[groupID]) {
          bin.values[groupID] = 1
        } else {
          bin.values[groupID] += 1
        }
      }

      // Next, build up a tabular representation of each of these bins by group
      const groupIDs = Array.from(new Set(groupColData))

      const xMinData: number[] = []
      const xMaxData: number[] = []
      const yMinData: number[] = []
      const yMaxData: number[] = []
      const countData: number[] = []
      const fillData: number[] = []

      for (let i = 0; i < groupIDs.length; i++) {
        const groupID = groupIDs[i]

        for (const bin of bins) {
          const count = bin.values[groupID] || 0

          let yMin = 0

          if (position === 'stacked') {
            yMin = groupIDs
              .slice(0, i)
              .reduce((sum, k) => sum + (bin.values[k] || 0), 0)
          }

          xMinData.push(bin.min)
          xMaxData.push(bin.max)
          yMinData.push(yMin)
          yMaxData.push(yMin + count)
          countData.push(count)
          fillData.push(groupID)
        }
      }

      const binTable = newTable(binCount * groupIDs.length)
        .addColumn(X_MIN, xOriginalColType, xColType, xMinData)
        .addColumn(X_MAX, xOriginalColType, xColType, xMaxData)
        .addColumn(Y_MIN, 'system', 'number', yMinData)
        .addColumn(Y_MAX, 'system', 'number', yMaxData)
        .addColumn(COUNT, 'system', 'number', countData)
        .addColumn(FILL, 'system', 'number', fillData)

      return binTable
    }

    const createBins = (
      xDomain: number[],
      binCount: number
    ): Array<{max: number; min: number; values: {}}> => {
      const domainWidth = xDomain[1] - xDomain[0]
      const binWidth = domainWidth / binCount

      let binMinimums = range(xDomain[0], xDomain[1], binWidth)

      // Work around [an issue in d3-array][0] where the `stop` value for `range`
      // is inclusive due to floating point inaccuracies, even though it is
      // expected to be exclusive. Note that we don't use the recommended
      // workaround, since we wish to handle the case where the `domainWidth` is
      // less than 0.
      //
      // [0]: https://github.com/d3/d3-array/issues/5#issuecomment-132788501
      binMinimums = binMinimums.slice(0, binCount)

      const bins = binMinimums.map((min, i) => {
        const isLastBin = i === binMinimums.length - 1
        const max = isLastBin ? xDomain[1] : binMinimums[i + 1]

        return {min, max, values: {}}
      })

      return bins
    }