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pythonnumpyargmax
Harry Spratt
Harry Spratt

Reputation: 305

How to return the positions of the maximum value in an array

As stated I want to return the positions of the maximum value of the array. For instance if I have the array:

A = np.matrix([[1,2,3,33,99],[4,5,6,66,22],[7,8,9,99,11]])

np.argmax(A) returns only the first value which is the maximum, in this case this is 4. However how do I write code so it returns [4, 13]. Maybe there is a better function than argamax() for this as all I actually need is the position of the final maximum value.

Upvotes: 0

Views: 267

Answers (2)

fountainhead
fountainhead

Reputation: 3722

Since you mentioned that you're interested only in the last position of the maximum value, a slightly faster solution could be:

A.size - 1 - np.argmax(A.flat[::-1])

Here:

A.flat is a flat view of A.

A.flat[::-1] is a reversed view of that flat view.

np.argmax(A.flat[::-1]) returns the first occurrence of the maximum, in that reversed view.

Upvotes: 1

recentadvances
recentadvances

Reputation: 177

Find the max value of the array and then use np.where.

>>> m = a.max()
>>> np.where(a.reshape(1,-1) == m)
(array([0, 0]), array([ 4, 13]))

After that, just index the second element of the tuple. Note that we have to reshape the array in order to get the indices that you are interested in.

Upvotes: 1

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