Find the row indexes of several values in a numpy array

Question

I have an array X:

X = np.array([[4,  2],
              [9,  3],
              [8,  5],
              [3,  3],
              [5,  6]])

And

Answer 1

Here is a pretty fast solution that scales up well using numpy and hashlib. It can handle large dimensional matrices or images in seconds. I used it on 520000 X (28 X 28) array and 20000 X (28 X 28) in 2 seconds on my CPU

Code:

import numpy as np
import hashlib


X = np.array([[4,  2],
              [9,  3],
              [8,  5],
              [3,  3],
              [5,  6]])

searched_values = np.array([[4, 2],
                            [3, 3],
                            [5, 6]])

#hash using sha1 appears to be efficient
xhash=[hashlib.sha1(row).digest() for row in X]
yhash=[hashlib.sha1(row).digest() for row in searched_values]

z=np.in1d(xhash,yhash)  

##Use unique to get unique indices to ind1 results
_,unique=np.unique(np.array(xhash)[z],return_index=True)

##Compute unique indices by indexing an array of indices
idx=np.array(range(len(xhash)))
unique_idx=idx[z][unique]

print('unique_idx=',unique_idx)
print('X[unique_idx]=',X[unique_idx])

Output:

unique_idx= [4 3 0]
X[unique_idx]= [[5 6]
 [3 3]
 [4 2]]