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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!
456
NumPy arrays can be sorted by a single column, row, or by multiple columns or rows using the argsort() function. The argsort function returns a list of indices that will sort the values in an array in ascending value.
Use numpy. ndarray. sort() to sort a NumPy array in descending order. Use the syntax array[::-1] to reverse array .
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]])
>>>
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