2D Histogram

from dataviz import hist2d, save
from dataviz import Theme
from dataviz.core.colormaps import viridis

def main() raises:
    # Twenty thousand sensor readings that fall in two clusters,
    # one tight and one spread out; as a scatter they would be a
    # blob. A small linear congruential generator keeps the
    # example self-contained.
    var seed = 12345
    var xs = List[Float64]()
    var ys = List[Float64]()
    for i in range(20000):
        var u = List[Float64]()
        for _ in range(6):
            seed = (seed * 1103515245 + 12345) % 2147483648
            u.append(Float64(seed % 10000) / 10000.0 - 0.5)
        # Sums of uniforms are bell-shaped, which is all the
        # example needs.
        var gx = u[0] + u[1] + u[2]
        var gy = u[3] + u[4] + u[5]
        if i % 3 == 0:
            xs.append(2.0 + 0.6 * gx)
            ys.append(7.0 + 0.6 * gy)
        else:
            xs.append(6.0 + 2.2 * gx + 0.8 * gy)
            ys.append(3.0 + 1.6 * gy)
    var chart = hist2d(
        xs,
        ys,
        bins=40,
        theme=Theme(color_ramp=viridis()),
        title="Illustrative Sensor Readings, Binned",
        x_title="Reading A",
        y_title="Reading B",
    )
    save(chart, "docs/src/examples/out_hist2d.svg")