plot selected rows of numpy array

Question

Consider a small numpy array:

array([[  0.,   1.,   0.,   1.,   0.,   0.,   0.,   0.,   0.,   1.],
   [  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.],
   [  0.,   0.,   0.,   0.,  18.,  15.,  25.,   0.,   0.,   0.],
   [  0.,   0.,   0.,  23.,  19.,  20.,  20.,   0.,   0.,   0.],
   [  0.,   0.,  20.,  22.,  26.,  23.,  18.,   0.,   0.,   0.],
   [  0.,   0.,   0.,  23.,  16.,  20.,  13.,   0.,   0.,   0.],
   [  0.,   0.,   0.,   0.,  18.,  20.,  18.,   0.,   0.,   0.],
   [  0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.,   0.],
   [  0.,   1.,   0.,   0.,   1.,   0.,   0.,   0.,   0.,   0.]])

I would like to plot, let say from the row number 3 to the row number 6, i.e. a section of my numpy array(I am coming from matlab backgroud). How could I loop this? or How could I plot multiple rows of my numpy array in the same graph?

So far I have tried; I define an arbitrary x:

x = np.arange(0,10)

then If I use

plt.plot(x,data[3,:])

to plot the third row and It does fine. The problem arises if I try:

plt.plot(x,data[3:4,:])

I get the error "x and y must have same first dimension", which I understand because he stacks row number 3 and row number 4 together, so that x and y do not have the same dimension. How can I overcome that?

Thank you

you would like to plot row number 3 to row number 6 with what? I mean, do you need to plot row3 vs row6 or row3-row6 vs something else? — Srivatsan
– Srivatsan, Commented Oct 2, 2014 at 8:36
from row number 3 to row number 6 vs an arbitrary x contaning the same number elements (10) in a row — diegus
– diegus, Commented Oct 2, 2014 at 11:21

pseudocubic · Accepted Answer · 2014-10-02 13:50:43Z

4

As the error implies, your data.shape = (1,10) is inconsistent with your input x.shape = (10,). To solve this problem you can just transpose your data using .T, i.e.

plt.plot(x, data[3:4,:].T)

Also, keep in mind that data[3:4,:] is the same as data[3,:], you will need to use data[3:5,:] to get the 3rd and 4th rows, for example.

answered Oct 2, 2014 at 13:50

pseudocubic

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Srivatsan · Accepted Answer · 2014-10-02 14:04:00Z

2

Just a better application of psuedocubi's answer.

import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0,10,10)
y = np.array(YOUR DATA HERE)

plt.plot(x,a[3:4].T,'r--',label="x vs y1") #CONTAINS YOUR 3RD ROW
plt.plot(x,a[4:5].T,'g--',label="x vs y2") #CONTAINS YOUR 4TH ROW
plt.plot(x,a[5:6].T,'b--',label="x vs y3") #CONTAINS YOUR 5TH ROW
plt.legend(loc='best')
plt.xlabel("x")
plt.ylabel("y")
plt.show()

YOUR DATA PLOTTED WITH ARBITARY X

The x here as been plotted with your own data!

answered Oct 2, 2014 at 14:04

Srivatsan

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Comments

George · Accepted Answer · 2014-10-02 14:09:19Z

2

You can try:

for i in range(3):
    plt.plot( x , data[ i , : ] )

plt.show()

If you want a range of rows ,for example from 3 to 6 , you can use:

range(3,7,1) , where 1 is the step , 3 is the starting row and 7 is the last row we want to plot (6 ) plus one

edited Oct 2, 2014 at 14:09

answered Oct 2, 2014 at 13:50

George

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1 Comment

diegus Over a year ago

It is not really what I am looking for..It works for the first 3 rows but I want to plot from row number 3 to number 6, How can I do that with a similar loop?

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