plotting matplotlib from nump ndarray

Question

This is embarrassing, but I am unable to plot this:

  import numpy as np
  import matplotlib.pyplot as plt
  datf=np.loadtxt(filename, dtype=float,delimiter=" ")
  print((datf))
  plt.plot(datf[:0], datf[:1])
  plt.show()

This is datf:

[[  1.         19.778986 ]
 [  1.3625678  -1.9363698]
 [  1.4142136   6.5144132]
 [  1.6901453   3.8092139]
 [  2.         -4.0222051]]

And the error is:

ValueError: x and y must have same first dimension

Michael · Accepted Answer · 2017-03-22 18:22:17Z

2

It looks like you are trying to plot the first column as x and the second column as y. You made a mistake in indexing. To get the first column of datf, you need to do datf[:, 0] (note the comma).

Your final code will look like:

  import numpy as np
  import matplotlib.pyplot as plt
  datf=np.loadtxt(filename, dtype=float,delimiter=" ")
  print((datf))
  plt.plot(datf[:, 0], datf[:, 1])  # note the commas here
  plt.show()

answered Mar 22, 2017 at 18:22

Michael

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1 Comment

BaRud Over a year ago

Thanks a lot. I missed that, and had no clue why this trivial thing is not working

Gautham Kumaran · Accepted Answer · 2017-03-22 18:25:29Z

0

to get the 1st and 2nd column, indexing must be

plt.plot(datf[:,0],datf[:,1])

answered Mar 22, 2017 at 18:25

Gautham Kumaran

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