问题描述:

I have this following numpy matrix that I want to sort in ascending order based on the 3rd column values.

[[ 3.05706500e+06 4.98000000e+01 -2.62500070e+01 -9.38135544e+01]

[ 3.05706600e+06 4.98000000e+01 -3.00000056e+01 -9.38135544e+01]

[ 3.05706700e+06 4.98000000e+01 -3.37500042e+01 -9.38135544e+01]

[ 3.05706800e+06 4.98000000e+01 -3.75000028e+01 -9.38135544e+01]]

This is the matrix I actually want.

[[ 3.05706800e+06 4.98000000e+01 -3.75000028e+01 -9.38135544e+01]

[ 3.05706700e+06 4.98000000e+01 -3.37500042e+01 -9.38135544e+01]

[ 3.05706600e+06 4.98000000e+01 -3.00000056e+01 -9.38135544e+01]

[ 3.05706500e+06 4.98000000e+01 -2.62500070e+01 -9.38135544e+01]]

How do I do this using just numpy? Any help would be appreciated. Thanks!

网友答案:

Given your array

>>> arr
array([[  3.05706500e+06,   4.98000000e+01,  -2.62500070e+01,
         -9.38135544e+01],
       [  3.05706600e+06,   4.98000000e+01,  -3.00000056e+01,
         -9.38135544e+01],
       [  3.05706700e+06,   4.98000000e+01,  -3.37500042e+01,
         -9.38135544e+01],
       [  3.05706800e+06,   4.98000000e+01,  -3.75000028e+01,
         -9.38135544e+01]])

you can simply use numpy.sort with axis=0 to sort it as desired

>>> numpy.sort(arr,axis=0)
array([[  3.05706500e+06,   4.98000000e+01,  -3.75000028e+01,
         -9.38135544e+01],
       [  3.05706600e+06,   4.98000000e+01,  -3.37500042e+01,
         -9.38135544e+01],
       [  3.05706700e+06,   4.98000000e+01,  -3.00000056e+01,
         -9.38135544e+01],
       [  3.05706800e+06,   4.98000000e+01,  -2.62500070e+01,
         -9.38135544e+01]])
>>> 

I believe my previous answer was wrong as I misunderstood the question. Here is the correct answer

>>> arr[arr[:,2].argsort()]
array([[  3.05706800e+06,   4.98000000e+01,  -3.75000028e+01,
         -9.38135544e+01],
       [  3.05706700e+06,   4.98000000e+01,  -3.37500042e+01,
         -9.38135544e+01],
       [  3.05706600e+06,   4.98000000e+01,  -3.00000056e+01,
         -9.38135544e+01],
       [  3.05706500e+06,   4.98000000e+01,  -2.62500070e+01,
         -9.38135544e+01]])
>>> 
网友答案:

Use numpy.sort with the axis keyword to set the axis you want to sort by.

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