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How to find second largest value in an array?

Asked by Minu
on 7 Jun 2013
Latest activity Answered by Fernando
on 17 Nov 2014


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?



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3 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]);


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.

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

  1 Comment

per isakson
on 7 Jun 2013

I got your point.

Answer by Fernando
on 17 Nov 2014

function [ y ] = second_min( x )

 y = min(x(x>min(x)));



function [ y ] = second_max( x )

 y = max(x(x<max(x)));



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