Boxplot with variable length data in matplotlib

Question

I have collected some data in a textfile and want to create a boxplot. But this datafile contains rows of variable length, for example.

1.2, 2.3, 3.0, 4.5  
1.1, 2.2, 2.9

for equal length I could just do

PW  = numpy.loadtxt("./learning.dat")  
matplotlib.boxplot(PW.T);

How do I handle variable length data lines?

Answer 1

Just use a list of arrays or lists. boxplot will take any sort of sequence (Well, anything that has a __len__, anyway. It won't work with generators, etc.).

E.g.:

import matplotlib.pyplot as plt
x = [[1.2, 2.3, 3.0, 4.5],
     [1.1, 2.2, 2.9]]
plt.boxplot(x)
plt.show()

If you're asking how to read in your data, there are plenty of ways to do what you want. As a simple example:

import matplotlib.pyplot as plt
import numpy as np

def arrays_from_file(filename):
    """Builds a list of variable length arrays from a comma-delimited text file"""
    output = []
    with open(filename, 'r') as infile:
        for line in infile:
            line = np.array(line.strip().split(','), dtype=np.float)
            output.append(line)
    return output

plt.boxplot(arrays_from_file('test.txt'))
plt.show()