How can I find the index of the maximum element in an array without looping?
如何在不使用循环的情况下找到数组中最大元素的索引?
For example, if I have:
例如，如果我有:
a = [1 2 999 3];I want to define a function indexMax so that indexMax(a) would return 3.
我想定义一个函数indexMax，这样indexMax(a)会返回3。
Likewise for defining indexMin.
定义indexMin同样。
3 个解决方案
#1
21
As pointed by Evgeni max and min can return the argmax and argmin as second arguments.
It is worth while noting that you can use these functions along specific dimensions:
如Evgeni max和min所指出的，可以返回argmax和argmin作为第二个参数。值得注意的是，您可以沿着特定的维度使用这些功能:
A = rand(4); % 4x4 matrix [ row_max row_argmax ] = max( A, [], 2 ); % max for each row - 2nd dimension [ col_min col_argmin ] = min( A, [], 1 ); % min for each column - 1st dimensionNote the empty [] second argument - it is crucial max( A, [], 2 ) is not at all equivalent to max( A, 2 ) (I'll leave it to you as a small exercise to see what max( A, 2 ) does).
注意这个空的[]第二个参数——max(A，[]， 2)根本不等于max(A, 2)(我把它留给你作为一个小练习，看看max(A, 2)做什么)。
The argmax/argmin returned from these "along dimension" calls are row/col indices.
这些“沿着维度”调用返回的argmax/argmin是行/col索引。
#2
25
The built-in max function has this functionality when two output arguments are specified:
当指定两个输出参数时，内置的max函数具有以下功能:
a = [1 2 999 3];[the_max, index_of_max] = max(a)the_max = 999index_of_max = 3Likewise for min.
同样,分钟。
#3
7
Just as an alternative solution, you might try this:
作为一种替代方案，您可以尝试以下方法:
a = rand(1,1000);min_idx = find(a == min(a));Obviously, the same procedure is applicable in the case of max.
显然，同样的程序也适用于max。
I hope this helps.
我希望这可以帮助。
#1
21
As pointed by Evgeni max and min can return the argmax and argmin as second arguments.
It is worth while noting that you can use these functions along specific dimensions:
如Evgeni max和min所指出的，可以返回argmax和argmin作为第二个参数。值得注意的是，您可以沿着特定的维度使用这些功能:
A = rand(4); % 4x4 matrix [ row_max row_argmax ] = max( A, [], 2 ); % max for each row - 2nd dimension [ col_min col_argmin ] = min( A, [], 1 ); % min for each column - 1st dimensionNote the empty [] second argument - it is crucial max( A, [], 2 ) is not at all equivalent to max( A, 2 ) (I'll leave it to you as a small exercise to see what max( A, 2 ) does).
注意这个空的[]第二个参数——max(A，[]， 2)根本不等于max(A, 2)(我把它留给你作为一个小练习，看看max(A, 2)做什么)。
The argmax/argmin returned from these "along dimension" calls are row/col indices.
这些“沿着维度”调用返回的argmax/argmin是行/col索引。
#2
25
The built-in max function has this functionality when two output arguments are specified:
当指定两个输出参数时，内置的max函数具有以下功能:
a = [1 2 999 3];[the_max, index_of_max] = max(a)the_max = 999index_of_max = 3Likewise for min.
同样,分钟。
#3
7
Just as an alternative solution, you might try this:
作为一种替代方案，您可以尝试以下方法:
a = rand(1,1000);min_idx = find(a == min(a));Obviously, the same procedure is applicable in the case of max.
显然，同样的程序也适用于max。
I hope this helps.
我希望这可以帮助。