How to plot numpy array versus row number

Question

Assume we have a csv file with a single column. I can plot it with ;

data = np.loadtxt(file)
test = data[:,0]
plot(test)

and it plots test versus the row number (entries). But I want to multiply this row number so that I can plot ;

plot(test,row[i]*25)

I think there should exist a simple way than to arrayize the row number. Any pythonic way to handle this issue ?

Have a look at numpy.arange. E.g. y = 25 * np.arange(test.size). numpy.indices, numpy.mgrid, numpy.ogrid, numpy.ndindex, and numpy.ndenumerate are similar functions that are also useful to be aware of. — Joe Kington
– Joe Kington, Commented Apr 21, 2013 at 19:42

Stephane Rolland · Accepted Answer · 2013-04-21 21:22:50Z

4

given a data you can do :

import matplotlib.pyplot as plt

data=[0,2,113,....,19,5]
x_coordinate = [ 25 * i for i in range(len(data)) ]
plt.plot(x_coordinate,data)
plt.show()

you'll have all x label indexes as multiples of 25

or use the numpy array functionality:

x_coordinates = 25 * np.arange(test.size)

edited Apr 21, 2013 at 21:22

answered Apr 21, 2013 at 19:13

Stephane Rolland

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2 Comments

Benjamin Hodgson Over a year ago

This is OK but it's not vectorised.

Stephane Rolland Over a year ago

If by vectorized you mean using numpy array functionnality, I have edited the answer using the numpy array function x_coordinates = 25 * np.arange(test.size) like Joe Kington suggested you in the comments.

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