NumPy

numpy.argmax

numpy.argmax(a, axis=None, out=None)[source]

Returns the indices of the maximum values along an axis.

Parameters
aarray_like

Input array.

axisint, optional

By default, the index is into the flattened array, otherwise along the specified axis.

outarray, optional

If provided, the result will be inserted into this array. It should be of the appropriate shape and dtype.

Returns
index_arrayndarray of ints

Array of indices into the array. It has the same shape as a.shape with the dimension along axis removed.

See also

ndarray.argmax, argmin

amax

The maximum value along a given axis.

unravel_index

Convert a flat index into an index tuple.

take_along_axis

Apply np.expand_dims(index_array, axis) from argmax to an array as if by calling max.

Notes

In case of multiple occurrences of the maximum values, the indices corresponding to the first occurrence are returned.

Examples

>>> a = np.arange(6).reshape(2,3) + 10
>>> a
array([[10, 11, 12],
       [13, 14, 15]])
>>> np.argmax(a)
5
>>> np.argmax(a, axis=0)
array([1, 1, 1])
>>> np.argmax(a, axis=1)
array([2, 2])

Indexes of the maximal elements of a N-dimensional array:

>>> ind = np.unravel_index(np.argmax(a, axis=None), a.shape)
>>> ind
(1, 2)
>>> a[ind]
15
>>> b = np.arange(6)
>>> b[1] = 5
>>> b
array([0, 5, 2, 3, 4, 5])
>>> np.argmax(b)  # Only the first occurrence is returned.
1
>>> x = np.array([[4,2,3], [1,0,3]])
>>> index_array = np.argmax(x, axis=-1)
>>> # Same as np.max(x, axis=-1, keepdims=True)
>>> np.take_along_axis(x, np.expand_dims(index_array, axis=-1), axis=-1)
array([[4],
       [3]])
>>> # Same as np.max(x, axis=-1)
>>> np.take_along_axis(x, np.expand_dims(index_array, axis=-1), axis=-1).squeeze(axis=-1)
array([4, 3])

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