Get index of an array in a numpy array

Question

I have a spectrogram. It's 129 rows x n columns. I want to "cut" the columns to 20. And I would do something like this:

if spectrogram.shape[1] > 20:
                  for row in spectrogram:
                    i = spectrogram.index(row)
                    row = row[:20]
                    spectrogram[i] = row

But it throws out an error using .index(), so I tried using .where() as I saw here on SOF but another error occurred:

AttributeError: 'numpy.ndarray' object has no attribute 'where'

How should I do?

when it comes to numpy, you have much better choices than iteration. in this case, you can slice like spectrogram[:, :20] — Paritosh Singh
– Paritosh Singh, Commented Jun 18, 2019 at 7:33
Thank you guys, gonna accept the answer in the bottom. But your works too :) — Francesco Buccoliero
– Francesco Buccoliero, Commented Jun 18, 2019 at 7:37

Mark · Accepted Answer · 2019-06-18 07:33:11Z

1

You should be able to just take the slice you want without the loop (whenever you're tempted to loop over a numpy array, there's usually a better way).

spectrogram[:, :20]

Here's a simplified example: given a 5x10 array, take just the first 5 of each row giving you a 5x5 array:

import numpy as np
a = np.arange(50).reshape(5, 10)
a[:, :5]

result

array([
   [ 0,  1,  2,  3,  4],
   [10, 11, 12, 13, 14],
   [20, 21, 22, 23, 24],
   [30, 31, 32, 33, 34],
   [40, 41, 42, 43, 44]])

answered Jun 18, 2019 at 7:33

Mark

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