Question

existing Logarithmic Axis默认为10的底数。是否可以将小数位数更改为其他底数的对数？

Answer 1

您可以实现自定义比例来更改对数比例的基础，如下所示：

class Log2Axis extends Chart.Scale {
  constructor(cfg) {
    super(cfg);
    this._startValue = undefined;
    this._valueRange = 0;
  }

  parse(raw, index) {
    const value = Chart.LinearScale.prototype.parse.apply(this, [raw, index]);
    return isFinite(value) && value > 0 ? value : null;
  }

  determineDataLimits() {
    const {
      min,
      max
    } = this.getMinMax(true);
    this.min = isFinite(min) ? Math.max(0, min) : null;
    this.max = isFinite(max) ? Math.max(0, max) : null;
  }

  buildTicks() {
    const ticks = [];

    let power = Math.floor(Math.log2(this.min || 1));
    let maxPower = Math.ceil(Math.log2(this.max || 2));
    while (power <= maxPower) {
      ticks.push({
        value: Math.pow(2, power)
      });
      power += 1;
    }

    this.min = ticks[0].value;
    this.max = ticks[ticks.length - 1].value;
    return ticks;
  }

  /**
   * @protected
   */
  configure() {
    const start = this.min;

    super.configure();

    this._startValue = Math.log2(start);
    this._valueRange = Math.log2(this.max) - Math.log2(start);
  }

  getPixelForValue(value) {
    if (value === undefined || value === 0) {
      value = this.min;
    }

    return this.getPixelForDecimal(value === this.min ? 0 :
      (Math.log2(value) - this._startValue) / this._valueRange);
  }

  getValueForPixel(pixel) {
    const decimal = this.getDecimalForPixel(pixel);
    return Math.pow(2, this._startValue + decimal * this._valueRange);
  }
}

Log2Axis.id = 'log2';
Log2Axis.defaults = {};

Chart.register(Log2Axis);

var options = {
  type: 'line',
  data: {
    labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange", "Black", "White"],
    datasets: [{
      label: '# of Votes',
      data: [8, 3, 60, 20, 130, 80, 1030, 250],
      backgroundColor: 'pink',
      borderColor: 'pink'
    }]
  },
  options: {
    scales: {
      x: {
        display: true
      },
      y: {
        display: true,
        type: 'log2',
      }
    }
  }
}

var ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);

<body>
  <canvas id="chartJSContainer" width="600" height="400"></canvas>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.4.0/chart.js"></script>
</body>

小提琴链接：https://jsfiddle.net/Leelenaleee/oyLf0wed/6/

感谢为此制作示例的 chart.js 团队：https://www.chartjs.org/docs/master/samples/advanced/derived-axis-type.html

在Chart.js中更改对数刻度的基数

1 个答案: