How to detect and mask missing data on imported csv files in Python?
<p>I am very new to Python and I have been trying to detect missing data in lists created from data in imported csv files so that I can plot the series using matplotlib without getting an error.</p>

<p>I show you what I have:</p>

<pre><code>import numpy as np
# import matplotlib.pyplot as plt
import csv
from pylab import *

res = csv.reader(open('cvs_file_with_data.csv'), delimiter=',')
res.next() # do not read header

ColOneData = []
ColTwoData = []
ColThreeData = []

for col in res:
    ColOneData.append(col[0])
    ColTwoData.append(col[1])
    ColThreeData.append(col[2])

print ColOneData # I got here the following ['1', '2', '3', '4', '5'] 

print ColTwoData # I got here the following ['1', '2', '', '', '5']

print ColThreeData # I got here the following ['', '', '3', '4', '']

ColTwoData_M = np.ma.masked_where(ColTwoData == '', ColTwoData) # This does not work
</code></pre>

<p>I need to mask the empty values e.g. '' so that I can plot the series without errors. Any suggestion to solve this problem?</p>

<p>Regards...</p>
