Sorting 2d array by rows in python

Question

I would like to rearrange the rows in a python numpy array according to descending order of the first column. For Example,

([[2,3,1,8],
  [4,7,5,20],
  [0,-2,2,0]])

to be converted to

([[0,-2,2,0],
  [2,3,1,8],
  [4,7,5,20]])

such that first column converts to [0,2,4] from [2,4,0]

Does this answer your question? Sorting arrays in NumPy by column — adir abargil
– adir abargil, Commented Dec 20, 2020 at 6:33

U13-Forward · Accepted Answer · 2020-12-20 05:03:31Z

3

Regular sorted does it:

print(sorted([[2,3,1,8], [4,7,5,20], [0,-2,2,0]]))

But if you only want to sort by the first columns, use:

print(sorted([[2,3,1,8], [4,7,5,20], [0,-2,2,0]], key=lambda x: x[0]))

They both output:

[[0, -2, 2, 0], [2, 3, 1, 8], [4, 7, 5, 20]]

answered Dec 20, 2020 at 5:03

U13-Forward

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Comments

adir abargil · Accepted Answer · 2020-12-20 06:08:07Z

3

If you intend to get numpy operation:

arr = arr[arr[:,0].argsort()]

answered Dec 20, 2020 at 5:56

adir abargil

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