Numpy Array Descending Sort Like Table (Move Entire Column)

Question

How do I make this numpy array:

[[   0.    1.    2.]
 [ 192.  312.  98.]]

Get sorted into this:

[[   1.    0.    2.]  # Moves entire column instead of just the value in the second row
 [ 312.  192.  98.]]  # Highest to lowest

Thank you.

akuiper · Accepted Answer · 2017-07-20 20:28:24Z

3

Use argsort on the second row and then use the output indices to reorder columns:

a[:, a[1].argsort()[::-1]]
#array([[   1.,    0.,    2.],
#       [ 312.,  192.,   98.]])

answered Jul 20, 2017 at 20:28

akuiper

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3 Comments

Mr_U4913 Over a year ago

I have a question. when you a[:, [1,0,2]], [1,0,2] helps you order the second row. But I do not understand why the first row will change according to the second row' order.....

akuiper Over a year ago

@Mr_U4913 Because you are slicing the first dimension with :, so the order applys to all rows. regardless of first row or second row.

Elliot Killick Over a year ago

Wow, thanks. Couldn't have asked for a better answer! Worked for me running Python 3.5.3 and numpy 1.13.0.

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