CODEWITHSUNDEEP
matlab
Yuseferi
Yuseferi

Reputation: 8670

get second max element in matlab

I have an array, say A = [ 3 5 6 7 ]. I know I can get the maximum value of this array with max(A) and it returns 7, but how can I get the second max (6) from this array without sorting or removing the first maximum value?

Upvotes: 4

Views: 23137

Answers (3)

Barney Szabolcs
Barney Szabolcs

Reputation: 12514

First of all, unless you have really-really large vectors, use unique and get the second last index.

If you wish to preserve the max element and you vector does not contain NaN's you can try:

[max_value,max_idx] = max(A);  % [3 5 6 7]
A(idx) = NaN;              % [3 5 6 NaN]
second_max_value = max(A); % 6
A(idx) = max_value;        % [3 5 6 7]

If you have multiple indices with the same max value, it is your choice to include

if length(max_idx)>1, second_max_value=max_value, end

UPDATE:

According to the comment of the OP next to the question, let me add:

You can also use sort without changing the original array:

[~, idx] = sort(A);
A(idx(end)) % is the max value
A(idx(end-1)) % is the second max value

Upvotes: 7

Danil Asotsky
Danil Asotsky

Reputation: 1241

I can propose following tricky solution:

second_max_value = max(A(A~=max(A)))

Here A(A~=max(A)) will be temporary array that not contain maximal value of original array. Than you receive maximum of this array.

Upvotes: 8

Acorbe
Acorbe

Reputation: 8391

What about 

        B = unique(A);      % // Finds unique values and sorts
        max_2 = B(end-1);   % // Second maximum

?

test:

     A= [ 3 5 6 7  2 4]
     B = unique(A)
     B(end-1)

        ans =

            6

Upvotes: 2

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