Question

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.

I show you what I have:

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

I need to mask the empty values e.g. ” so that I can plot the series without errors. Any suggestion to solve this problem?

Regards…

Answer 1

What do you mean by mask? Remove? If so, try the following:

masked_data = [point for point in data if point != '']

Edit:

I’m not used to numpy, but maybe this is what you are searching for:

>>> data = numpy.array(['0', '', '1', '', '2'])
>>> numpy.ma.masked_where(data == '', data)
masked_array(data = [0 -- 1 -- 2],
             mask = [False True False True False],
       fill_value = N/A)