How to select 2nd largest number (or largest if no 2nd largest)

I need to find the second largest number in a vector but the number of elements from 4 to 1 so sometimes there is no second largest number (only the largest number) and in this case I can use the largest number.

I started with b=sort(a) c=(b(:,end-1)

but obviously I get an error when there is only 1 element.

Sorry if I am missing the obvious here!

[Julie]

many thanks, it worked beautifully, esp using 'unique' for those pesky duplcates values!

Answer 1

[Matt Tearle]

Is it possible to have repeated values? If so, what do you define as the "second largest" value? Eg secondmax([1 2 3 3]) = 2? or 3?

y = [x(1),unique(x)];
z = y(end-1);

gives the first option. Replacing unique with sort gives the second.

Answer 2

[Wayne King]

Hi Julie, one simple way is

N = 1;
x = randn(N,1);
b = sort(x,'descend');
if (length(b)>1)
b(2)
else
b(1)
end

[Wayne King]

Obviously, you can change N above to something greater than 1, e.g. N = 4

Answer 3

[Jan]

There are some methods:

b = sort(a);
c = b(max(1, end-1));

Or:

b = sort(a, 'descending');
c = b(max(2, length(b)));

Or:

if length(a) == 1
  c = a;
else
  b = sort(a, 'descending');
  c = b(2);
end