Question

I have a data file, which I need to read. I know to read files in Python you have to do something like:

file = open(fileLocaion, 'r+')

But I do not know who to do special reads. The data I have is in columns. So x values in one column and y values in another with headers at the top. The data (my text file a.txt) looks like

 Charge (1x), Ch A, Run #1
 Time ( s ) Charge (1x) ( µC )
 0.0000 0.021
 0.1000 0.021
 0.2000 0.021
 0.3000 0.021
 0.4000 0.021
 0.5000 0.021
 0.6000 0.021

So the first time value is 0.0000 and the first charge value is 0.021. I want to be able to take this into Python and use matplotlib to plot it. But I am having trouble figuring out how to read this data.

Answer 1

If you’re going to be plotting it with matplotlib, probably the simplest thing to do is to use numpy.loadtxt [docs], because you’ll have numpy installed anyway:

>>> import numpy
>>> d = numpy.loadtxt("mdat.txt", skiprows=2)
>>> d
array([[ 0.   ,  0.021],
       [ 0.1  ,  0.021],
       [ 0.2  ,  0.021],
       [ 0.3  ,  0.021],
       [ 0.4  ,  0.021],
       [ 0.5  ,  0.021],
       [ 0.6  ,  0.021]])

Note that I had to add skiprows=2 here to skip the header. Then the times are d[:,0] and the charges d[:,1], or you could get them explicitly with loadtxt:

>>> times, charges = numpy.loadtxt("mdat.txt", skiprows=2, unpack=True)
>>> times
array([ 0. ,  0.1,  0.2,  0.3,  0.4,  0.5,  0.6])
>>> charges
array([ 0.021,  0.021,  0.021,  0.021,  0.021,  0.021,  0.021])