Heatmaps in Python

imshow draws a matrix; the colorbar and the ticks make it legible.

import matplotlib

matplotlib.use("Agg")
import matplotlib.pyplot as plt
import numpy as np

langs = ["python", "rust", "sql"]
days = ["mon", "tue", "wed"]
grid = np.array([[88, 97, 104], [80, 85, 91], [70, 76, 79]])

figure, axes = plt.subplots()
image = axes.imshow(grid, cmap="magma")
axes.set_xticks(range(len(days)), labels=days)
axes.set_yticks(range(len(langs)), labels=langs)
for row in range(grid.shape[0]):
    for col in range(grid.shape[1]):
        axes.text(col, row, grid[row, col], ha="center", va="center",
                  color="white", fontsize=8)
figure.colorbar(image, ax=axes, label="tpm")
figure.savefig("heatmap.png")

How it works

1. imshow maps values to colors over a grid.
2. Set both tick sets, or the axes lie about the labels.
3. Writing the number in each cell beats guessing from the color.

Keywords and builtins used here

• as
• for
• len
• range

The run, in numbers

Lines

20

Characters to type

613

Tokens

224

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 128 seconds.

Type this snippet

Step 5 of 5 in Plot types, step 9 of 14 in Plotting with matplotlib.

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