2D Histogram

Histogram on a regular two-dimensional grid.

The x-axis and y-axis define the bin edges. As illustrated in this example, the bin widths are not necessarily identical.

@NX_class = "NXroot"
@default = "scan1"
scan1:
  @NX_class = "NXentry"
  @default = "data"
  data:
    @NX_class = "NXdata"
    @axes = ["y", "x"]
    @signal = "z"
    x: NX_FLOAT64[7]
    y: NX_FLOAT64[9]
    z: NX_FLOAT64[8,6]

Explanation:

1. @axes has two values which corresponds to the signal rank of two.

2. z is the default signal to be plotted versus x and y.

3. z has 6 rows and 8 columns.

4. y has one more value than the first dimension of z since it contains the bin edges.

5. x has one more value than the second dimension of z since it contains the bin edges.

# Data
import numpy as np

x = [-3.0, -2.5, -1.0, 0.0, 1.0, 2.5, 3.0]
y = [-3.0, -2.8, -1.3, -0.75, 0.0, 0.1, 1.5, 2.25, 3.0]

xx = np.linspace(-3, 3, 200)
yy = np.linspace(-3, 3, 200)
xx, yy = np.meshgrid(xx, yy)
zz = (1 - xx / 2 + xx**5 + yy**3) * np.exp(-(xx**2) - yy**2)
z, _, _ = np.histogram2d(yy.flatten(), xx.flatten(), bins=[y, x], weights=zz.flatten())

# Plot
import matplotlib.pyplot as plt  # noqa E402

plt.style.use("_mpl-gallery-nogrid")

fig, ax = plt.subplots()

mesh = ax.pcolormesh(x, y, z, edgecolor="k", linewidth=0.7, shading="flat")

plt.show()