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

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Julie
Julie 2011-9-30
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!

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采纳的回答

Matt Tearle
Matt Tearle 2011-9-30
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.

更多回答（2 个）

Wayne King
Wayne King 2011-9-30
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
Jan
Jan 2011-9-30
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

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