Method updateCircles

src/heatmap.ts:182–207

(container, points: Example2D[])

  }

  private updateCircles(container, points: Example2D[]) {
    // Keep only points that are inside the bounds.
    let xDomain = this.xScale.domain();
    let yDomain = this.yScale.domain();
    points = points.filter(p => {
      return p.x >= xDomain[0] && p.x <= xDomain[1]
        && p.y >= yDomain[0] && p.y <= yDomain[1];
    });

    // Attach data to initially empty selection.
    let selection = container.selectAll("circle").data(points);

    // Insert elements to match length of points array.
    selection.enter().append("circle").attr("r", 3);

    // Update points to be in the correct position.
    selection
      .attr({
        cx: (d: Example2D) => this.xScale(d.x),
        cy: (d: Example2D) => this.yScale(d.y),
      })
      .style("fill", d => this.color(d.label));

    // Remove points if the length has gone down.
    selection.exit().remove();
  }
}  // Close class HeatMap.

export function reduceMatrix(matrix: number[][], factor: number): number[][] {