n lowest values of a series

Hello, I'd like to find the n lowest values of a series of datas. "min" fonction does not seem to propose this option. I could use a loop of course, bur I'd like to find a fonction that could do that in 1 time if possible. Thank you for your help Christophe

Answer 1

[Jan]

For large data sets, sort is time-consuming. Then:

x            = rand(1, 1e6);
tic;
[min1, ind1] = min(x);
x(ind1)      = Inf;
[min2, ind2] = min(x);
y            = [min1, min2];
toc

tic;
x = sort(x);
y = x(1:2);
toc

I cannot measure it currently. What are your results?

[Wayne King]

Elapsed time is 0.148598 seconds.

Elapsed time is 0.109737 seconds.

R2012a - Windows 64-bit

[Sean de Wolski]

x = rand(1, 1e6);

t1 = 0;

t2 = 0;

for ii = 1:100

tic;

[min1, ind1] = min(x);

x(ind1) = Inf;

[min2, ind2] = min(x);

y = [min1, min2];

t1 = t1+toc;

tic

x = sort(x);

y = x(1:2);

t2 = t2+toc;

end

[t1 t2]

ans =

0.1765 3.4405

Answer 2

[Wayne King]

You can use sort() with the 'ascend' option.

     % find smallest 5 values
     n = 5;
     x = randn(100,1);
     y = sort(x,'ascend');
     y = y(1:n)

Answer 3

[Christophe]

Hello Wayne, Jan and Sean, Thanks for your answers. In fact I will use a loop (for) and Inf.

Answer 4

[Christophe]

Finally here is my solution :

x = rand(1, 1e6);
for m = 1:50
  [mini(m), ind(m)] = min(x);
  x(ind(m)) = Inf;
end