Plot with python

Question

Hello i know that this way to plot in matlab works:

subplot(2,2,[1, 2])
plot(Tabsauv(:, 2:2:2*Ntracks), Tabsauv(:, 3:2:(2*Ntracks+1)),couleur,'LineWidth',2, 'MarkerSize', 2)
grid('on')
hold on

When Tabasauv is a table of values.

I'm a new beginner in python, I tried to plot this in this way with python but it still not working, any idea?

 80 Ntracks=5
 81 fig= plt.figure()
 82 ax=fig.add_subplot(1,1,1)
 83
 84 data_1=np.array([:,2:2:(2*Ntracks)])
 85 data_2=np.array([:,3:2:(2*Ntracks+1])
 86 points = data[:,2:4]
 87
 88 color = np.sqrt((points**2).sum(axis = 1))/np.sqrt(2.0)
 89 rgb = plt.get_cmap('jet')(color)
 90
 91 ax.scatter(data_1, data_2, color = rgb)
 92 plt.show()

I got this error caus' i don't know how to translate it in python:

    data_1=np.arange([:,2:2:(2*Ntracks)])
                      ^
SyntaxError: invalid syntax

Thank you.

You would get an answer very quickly if you just (clearly) stated what you want np.arange([:,2:2:(2*Ntracks)]) to be. As it is, I added numpy and matlab to your tags so you might find someone who knows both (matlab was too many years ago for me). — tom10
– tom10, Commented Feb 3, 2014 at 16:22

Glorfindel · Accepted Answer · 2023-01-06 20:10:10Z

2

In matlab, you can generate arrays with ":". In python, you can create arrays using range() function or using arange (in numpy)

so,

 a = 3:5

in matlab is just the same as

a = np.arange(3,5) #or
a = np.array(range(3,5))

in Python.

Anyway, you might want to look at this page Link in order to translate you code \ thought patterns from Matlab to Numpy.

edited Jan 6, 2023 at 20:10

Glorfindel

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answered Feb 3, 2014 at 17:56

Ronen

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YS-L · Accepted Answer · 2014-02-03 16:35:43Z

0

You probably mean

data_1 = data[:,2:(2*Ntracks):2]

instead in your code, and similarly for data_2.

A few more things to note:

In numpy indices start from 0. data[:,1:] will skip the first column. Watch out for off-by-one error when doing the translation.
Slicing works slightly differently. The stride is specified by the last number, which is 2 in the above case, not the middle number (different from the Matlab convention).

edited Feb 3, 2014 at 16:35

answered Feb 3, 2014 at 16:24

YS-L

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