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How to find second largest value in an array?

Asked by Minu on 7 Jun 2013

Hi

I want to find the second largest and minimum value in array? A=[1;10;15;30;40;50;100].I want to get the result as Second minimum value=10 and second largest value=50 Help me plz...

1 Comment

Walter Roberson on 7 Jun 2013

What do you want to do if there are multiple instances of the maximum or minimum?

Minu

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2 Answers

Answer by Andrei Bobrov on 7 Jun 2013
Edited by Andrei Bobrov on 7 Jun 2013
Accepted answer
[ii,ii] = sort(A);
out = A(ii([2,end-1]));

for your example (A) just:

out = A([2,end-1]);

more variant

A1 = unique(A);
out = A1([2,end-1]);

4 Comments

Jan Simon on 7 Jun 2013

The sorting can be more expensive than searching the max twice:

[ignore, index] = max(A);
A(index) = -Inf;       % [EDITED], not +Inf!
max2 = max(A);

In this method Walter's suggestions must be considered also.

Walter Roberson on 7 Jun 2013

If the array is single precision or double precision, NaN is safer than Inf as there might be Inf in the array.

If the array is any of the other numeric data types, Inf will not exist and will be treated as the maximum numeric value for that datatype.

Jan Simon on 7 Jun 2013

Ficed typo: Of course -Inf is needed instead of +Inf to mask an existing maximium.

@Walter: Exactly. While the original message "A=[1;10;15;30;40;50;100]" looks like the OP talks about a double vector with finite values, the another type of input or values must be considered.

Even if another value is -Inf, my method replies the correct result. But NaN is the better choice.

Andrei Bobrov
Answer by Walter Roberson on 7 Jun 2013
for K = A
  if sum(A > K) == 1
    disp(K)
  end
end

1 Comment

per isakson on 7 Jun 2013

I got your point.

Walter Roberson

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