Scipy dendrogram leaf label colours

Question

Is it possible to assign colours to leaf labels of dendrogram plots from Scipy? I can't figure it out from the documentation. Here's what I've tried so far:

from scipy.spatial.distance import pdist, squareform
from scipy.cluster.hierarchy import linkage, dendrogram

distanceMatrix = pdist(subj1.ix[:,:3])
dendrogram(linkage(distanceMatrix, method='complete'), 
           color_threshold=0.3, 
           leaf_label_func=lambda x: subj1['activity'][x],
           leaf_font_size=12)

Thanks.

Answer 1

dendrogram uses matplotlib to create the plot, so after you've called dendrogram, you can manipulate the plot however you like. In particular, you can modify the attributes of the x axis labels, including the color. Here's an example:

import numpy as np
from scipy.cluster.hierarchy import dendrogram, linkage
import matplotlib.pyplot as plt


mat = np.array([[1.0,  0.5,  0.0],
                [0.5,  1.0, -0.5],
                [1.0, -0.5,  0.5],
                [0.0,  0.5, -0.5]])

dist_mat = mat
linkage_matrix = linkage(dist_mat, "single")

plt.clf()

ddata = dendrogram(linkage_matrix,
                   color_threshold=1,
                   labels=["a", "b", "c", "d"])

# Assignment of colors to labels: 'a' is red, 'b' is green, etc.
label_colors = {'a': 'r', 'b': 'g', 'c': 'b', 'd': 'm'}

ax = plt.gca()
xlbls = ax.get_xmajorticklabels()
for lbl in xlbls:
    lbl.set_color(label_colors[lbl.get_text()])

plt.show()

Here's the plot produced by the example: