Iterate through multidimensional numpy array and select values from a 1D array

Question

I have a one dimensional numpy array of shape (99,) which appears like the following:

[1 1 0 2 0 1 2 0 1 2 1 2 0 1 0 0 1 0 0 1 0 2 1 1 2 1 0 1 2 0 0 0 0 0 0 1 2
  1 1 0 1 1 2 1 1 0 1 0 1 2 0 0 2 0 1 1 2 0 2 0 2 0 2 0 0 2 1 0 0 0 1 0 2 1
1 0 0 1 1 1 0 1 1 1 2 2 0 0 2 0 1 1 1 2 2 2 0 2 1]

I would like to use the above array to select values from a multidimensional array of shape (99,3). Here are the first 5 rows of this array:

 array([[ 257.985,  332.58 , 2524.92 ],
   [ 254.29 ,  330.785, 2494.01 ],
   [ 253.81 ,  335.74 , 2499.5  ],
   [ 255.16 ,  336.7  , 2479.9  ],
   [ 249.98 ,  329.48 , 2451.32 ]])

I requesting coding help with this part. I'm looking to use the first array as an index to select values from the second multidim array shown above, creating a new array from this. For example, the first 5 values of this new array would be:

[332.58, 330.785, 253.81, 2479.9, 249.98, ...]

Mustafa Aydın · Accepted Answer · 2021-06-12 12:09:37Z

1

With "fancy" indexing:

multi_dim_arr[np.arange(len(multi_dim_arr)), one_dim_arr]

where multi_dim_arr is 99x3 matrix and one_dim_arr is 99-vector.

First set of indices goes from 0..98 others are your {0, 1, 2} indices from the 1D array. NumPy then selects pair-wise.

answered Jun 12, 2021 at 12:09

Mustafa Aydın

18.4k4 gold badges21 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Liam Spring · Accepted Answer · 2021-06-12 12:29:02Z

1

This is another way you can do this (it's more beginner-friendly):

import numpy as np

a = np.array([1, 1, 0, 2 ,0])

b =  np.array([[ 257.985,  332.58 , 2524.92 ],
   [ 254.29 ,  330.785, 2494.01 ],
   [ 253.81 ,  335.74 , 2499.5  ],
   [ 255.16 ,  336.7  , 2479.9  ],
   [ 249.98 ,  329.48 , 2451.32 ]])

c=[]
p = 0
for i in a:
    if i == 0:
        c.append(b[p][0])
    elif i == 1:
        c.append(b[p][1])
    else:
        c.append(b[p][2])
    p+=1

print(c)

answered Jun 12, 2021 at 12:29

Liam Spring

599 bronze badges

Collectives™ on Stack Overflow

Iterate through multidimensional numpy array and select values from a 1D array

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related