Unable to plot 4 histograms of iris dataset features using matplotlib - python-3.x

Question

using the iris dataset
import matplotlib.pyplot as plt
%matplotlib inline
import matplotlib
from sklearn import datasets
iris= datasets.load_iris()
x_index = 3
colors = ['blue', 'red', 'green']
for label, color in zip(range(len(iris.target_names)), colors):
plt.hist(iris.data[iris.target==label, x_index],
label=iris.target_names[label],
color=color)
plt.xlabel(iris.feature_names[x_index])
plt.legend(loc='upper right')
plt.show()
enter image description here
This code is plotting only one histogram with sepal length (image attached) as the x-axis.
To plot other features of iris dataset in a similar manner, I have to change the x_index to 1,2 and 3 (manually) and run this bit of code again.
To plot all four histograms simultaneously, I tried the following code:
import matplotlib.pyplot as plt
%matplotlib inline
import matplotlib
from sklearn import datasets
iris= datasets.load_iris()
fig, axes = plt.subplots(nrows= 2, ncols=2)
colors= ['blue', 'red', 'green', 'black']
x_index= 0
for ax in axes.flat:
for label, color in zip(range(len(iris.target_names)), colors):
ax= plt.hist(iris.data[iris.target==label, x_index], label=
iris.target_names[label], color=color)
plt.xlabel(iris.feature_names[x_index])
plt.legend(loc='upper right')
x_index+=1
plt.show()
This code gives me the following error:
IndexError: index 4 is out of bounds for axis 1 with size 4
Any advice?

Answer 1

Two issues:
ax is the name of the current axes in the loop. You should not redefine but instead use it as this is the axes you want to plot to. Replace ax = plt.hist by ax.hist.
x_index+=1 needs to be in the outer loop, not in the inner loop. Otherwise it will increment up to 11 instead of 3. Better get rid of it entirely and use a normal loop variable.
Complete code:
import matplotlib.pyplot as plt
from sklearn import datasets
iris= datasets.load_iris()
fig, axes = plt.subplots(nrows= 2, ncols=2)
colors= ['blue', 'red', 'green']
for i, ax in enumerate(axes.flat):
for label, color in zip(range(len(iris.target_names)), colors):
ax.hist(iris.data[iris.target==label, i], label=
iris.target_names[label], color=color)
ax.set_xlabel(iris.feature_names[i])
ax.legend(loc='upper right')
plt.show()