numpy.argmax — NumPy v2.2 Manual (original) (raw)

numpy.argmax(a, axis=None, out=None, *, keepdims=)[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.

keepdimsbool, optional

If this is set to True, the axes which are reduced are left in the result as dimensions with size one. With this option, the result will broadcast correctly against the array.

New in version 1.22.0.

Returns:

index_arrayndarray of ints

Array of indices into the array. It has the same shape as a.shapewith the dimension along axis removed. If keepdims is set to True, then the size of axis will be 1 with the resulting array having same shape as a.shape.

Notes

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

Examples

import numpy as np 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.amax(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.amax(x, axis=-1)

np.take_along_axis(x, np.expand_dims(index_array, axis=-1), ... axis=-1).squeeze(axis=-1) array([4, 3])

Setting keepdims to True,

x = np.arange(24).reshape((2, 3, 4)) res = np.argmax(x, axis=1, keepdims=True) res.shape (2, 1, 4)