#390 Basic radar chart

A radar chart displays the value of several numerical variables for one or several entities. Here is an example of a simple one, displaying the values of 5 variables for only one individual.

To my knowledge, there is no built in function allowing to make radar charts with Matplotlib. Thus, we have to use basic functions to build it, what makes it a bit fastidious.

The input data is a pandas data frame where each line represents an individual, and each column a variable. See graph #391 and #392 to see how to represent several individuals.

# Libraries
import matplotlib.pyplot as plt
import pandas as pd
from math import pi

# Set data
df = pd.DataFrame({
'group': ['A','B','C','D'],
'var1': [38, 1.5, 30, 4],
'var2': [29, 10, 9, 34],
'var3': [8, 39, 23, 24],
'var4': [7, 31, 33, 14],
'var5': [28, 15, 32, 14]
})

# number of variable
categories=list(df)[1:]
N = len(categories)

# We are going to plot the first line of the data frame.
# But we need to repeat the first value to close the circular graph:
values=df.loc[0].drop('group').values.flatten().tolist()
values += values[:1]
values

# What will be the angle of each axis in the plot? (we divide the plot / number of variable)
angles = [n / float(N) * 2 * pi for n in range(N)]
angles += angles[:1]

# Initialise the spider plot
ax = plt.subplot(111, polar=True)

# Draw one axe per variable + add labels labels yet
plt.xticks(angles[:-1], categories, color='grey', size=8)

# Draw ylabels
ax.set_rlabel_position(0)
plt.yticks([10,20,30], ["10","20","30"], color="grey", size=7)
plt.ylim(0,40)

# Plot data
ax.plot(angles, values, linewidth=1, linestyle='solid')

# Fill area
ax.fill(angles, values, 'b', alpha=0.1)