Annotation as symbols on a seaborn heatmap

Question

I want heatmap annotation as symbols. '*' at place of 1 and blank at 0.

import pandas as pd
import seaborn as sns
import matplotlib.pyplot as plt

x = pd.DataFrame({'a':[1,0,1,0]})
fig, (ax) = plt.subplots(ncols=1)
sns.heatmap(x, cmap="BuPu",annot=True,fmt='g',annot_kws={'size':10},ax=ax, yticklabels=[], cbar=False, linewidths=.5,robust=True, vmin=0, vmax=1)
plt.show()

Answer 1

The heatmap can only annotate with numbers. To put other text (or unicode symbols), ax.text can be used. The center of each cell is at 0.5 added to both the row and the column number.

import pandas as pd
import seaborn as sns
import matplotlib.pyplot as plt

x = pd.DataFrame({'a': [1, 0, 1, 0], 'b': [1, 1, 0, 1], 'c': [0, 1, 0, 0]})
fig, (ax) = plt.subplots(ncols=1)
sns.heatmap(x, cmap="BuPu", annot=False, ax=ax, yticklabels=[], cbar=False, linewidths=.5)

for i, c in enumerate(x.columns):
    for j, v in enumerate(x[c]):
        if v == 1:
            ax.text(i + 0.5, j + 0.5, '★', color='gold', size=20, ha='center', va='center')
plt.show()