How can I change the order of a 2D Array in Python

Question

Hi guys I have really simple question for you, let me explain shortly, for more detailed explanation please read below.

I want to order my 2D array which is an array of coordinates. However k= np.sort(k,0) is not working for me since it causes shuffling of y values. How can I solve this problem without losing my y values in an array of (x,y) ?

On the above you can see the result of np.sort(). It sorts all columns and shuffling the values, this makes the data useless.

Here is a longer explanation why I need that order:

I have a 2D array which are centers for K-means

centers = kmeans.cluster_centers_
plt.scatter(centers[:, 0], centers[:, 1], c='black', s=200, alpha=0.5);

I would like to sort this array with their x values because I want to use this in a RBF function like this:

plt.scatter(centers[:, 0], centers[:, 1], c='black', s=200, alpha=0.5);

rbfi = Rbf(centers[:, 0], centers[:, 1],function='gaussian')
u = rbfi(centers[:,0])
plt.plot(centers[:,0],u,'orange',linewidth=4)
plt.tick_params(labelcolor = 'white')

Since it is not ordered the function takes 2D points randomly and try to draw a line between them.

The result should look like something like this:

Hayden Eastwood · Accepted Answer · 2020-03-03 22:29:48Z

1

I'm assuming you mean that you want to keep the index unchanged. If that assumption is correct, I would suggest a dataframe, sorted with "inplace=True":

import dataframe as df
df = pd.DataFrame({'x': your_x_numpy_array, 'y': your_y_numpy_array})
df.sort_values(by=[your_index_of_choice],inplace = True)

answered Mar 3, 2020 at 22:29

Hayden Eastwood

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Ege · Accepted Answer · 2020-03-03 23:59:56Z

0

Here is my answer similar as @Hayden Eastwood

import pandas as pd
df = pd.DataFrame({'x': centers[:,0], 'y': centers[:,1]})
df = df.sort_values(by='x')
centers = pd.DataFrame(df).to_numpy()

And result:

answered Mar 3, 2020 at 23:59

Ege

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