Python random sample of two arrays, but matching indices

Question

I have two numpy arrays x and y, which have length 10,000. I would like to plot a random subset of 1,000 entries of both x and y. Is there an easy way to use the lovely, compact random.sample(population, k) on both x and y to select the same corresponding indices? (The y and x vectors are linked by a function y(x) say.)

Thanks.

Answer 1

You can use np.random.choice on an index array and apply it to both arrays:

idx = np.random.choice(np.arange(len(x)), 1000, replace=False)
x_sample = x[idx]
y_sample = y[idx]

Answer 2

Just zip the two together and use that as the population:

import random

random.sample(zip(xs,ys), 1000)

The result will be 1000 pairs (2-tuples) of corresponding entries from xs and ys.

Answer 3

After test numpy.random.choice solution, I found out it was very slow for larger array.

numpy.random.randint should be much faster

example

x = np.arange(1e8)
y = np.arange(1e8)
idx = np.random.randint(0, x.shape[0], 10000)
return x[idx], y[idx]

Answer 4

Using the numpy.random.randint function, you generate a list of random numbers, meaning that you can select certain datapoints twice.