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zxdawn opened this issue Oct 14, 2020 · 1 comment
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Wrong result of argsort for unsorted negative values #17561

zxdawn opened this issue Oct 14, 2020 · 1 comment
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@zxdawn
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zxdawn commented Oct 14, 2020

Reproducing code example:

import numpy as np

a = np.array([-9.93686340e+02, -9.85949280e+02, -9.67635925e+02, -9.39872864e+02,
              -8.98984009e+02, -8.41368530e+02, -7.81853699e+02, -6.92064392e+02,
              -6.12045349e+02, -5.30710449e+02, -4.54482269e+02, -3.71461731e+02,
              -3.14179626e+02, -2.76059692e+02, -2.41759018e+02, -2.20870255e+02,
              -1.92301758e+02, -1.66814026e+02, -1.44157349e+02, -1.30507690e+02,
              -1.12051003e+02, -9.58245697e+01, -8.61438751e+01, -7.31186905e+01,
              -6.15607414e+01, -4.49081726e+01, -3.38174362e+01, -2.26543159e+01,
              -1.42377014e+01, -8.23967838e+00, -4.27592516e+00, -1.91338563e+00,
              -6.95205748e-01, -1.86089307e-01, -0.00000000e+00,
              -9.93686328e+02, -7.39944519e+02])

print(np.argsort(a))

Error message:

[ 0 35  1  2  3  4  5  6 36  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21
 22 23 24 25 26 27 28 29 30 31 32 33 34]

The result should be:

[ 0  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21
 22 24 25 26 27 28 29 30 31 32 1 23]

Note that a[:-2] is ascending (print(np.argsort(a[:-2]))):

[ 0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
 24 25 26 27 28 29 30 31 32 33 34]

The last two elements cause the bug above.

NumPy/Python version information:

1.19.1 3.8.5 | packaged by conda-forge | (default, Jul 24 2020, 01:25:15) 
[GCC 7.5.0]
@eric-wieser
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eric-wieser commented Oct 14, 2020 •
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Duplicate of #8757

@eric-wieser eric-wieser marked this as a duplicate of #8757 Oct 14, 2020
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