comparison/checking without for loop

Hi there,

Say if I have a random event with just -1 and 1. e.g. a = randsrc(5,1);%that will generate a 5x1 matrix with just -1 or 1

Now say if I want to check how many of -1 or 1 in a, how can I do that without using for loop? I try to do this but doesn't work:

m =0;

if(a == 1)

m = m+1;

end

Any help would be really appreciated.

Cheers,

Rak

[Andrei Bobrov]

accumarray((a > 0) + 1,a)

Answer 1

[Geoff]

nneg = sum(a==-1);
npos = sum(a==1);

[Ricky]

Thanks Geoff,

How about if I want to assign something to r if a is 1 and to r1 if a is -1?

[Ricky]

say I have t0 and t1

and I want to assign r = t0 if a is 1 and r = t1 if a is -1?

[Geoff]

r(a==-1) = 0;

r(a==1) = 42;

This is called logical indexing... You can do whatever you like. The following example selects out of a only positive values less than 20:

a(a<20 & mod(a,2)==0)

And if you want to assign something different for every selected value, just use an array (or matrix) the same size as the number of selected items:

r(a==-1) = rand(1,sum(a==-1));

[Geoff]

Yes... replace '0' and '42' in my example with 't1' and 't0' respectively.

[Ricky]

Thanks Geoff!!