find is working in strange way

Hello I am trying to use the find to find number in array greater than 0.6 , but the behavior is strange

cluster_map=zeros(21,14);
[r c]=find(field>=0.6)

the length of the r is 20

cluster_map(r,c)=2;
[rr cc]=find(cluster_map == 2);

the length of rr is 40 !!! how this happen. I have attached the field array. thanks in advance

Answer 1

[Sean de Wolski]

r = [1 5 8]
c = [2 3 6]
x = zeros(10)
x(r,c) = 1

I'd guess what you want is to use sub2ind to use each combo of r and c once

x = zeros(10);
x(sub2ind(size(x),r,c)) = 1

[ahmed shaaban]

Yes , it works with the sub2ind , it is strange that when i put the indices directly that it makes all combination between them . Thanks a lot.

[Sean de Wolski]

It seems weird in this context. But consider this example:

x = zeros(5)
x(1:3,1:3) = 1

Would you expect the whole upper left corner to be ones, or just the upper left of the diagonal?

[ahmed shaaban]

what if the

if true
x=zeros(10,10,2);
end

with the same r and c , how we can use the sub2ind for the third dimension? Thanks in advance

[Sean de Wolski]

Fill the third-nth dimension with ones:

sub2ind(size(x),r,c,ones(size(r)))

[ahmed shaaban]

it just fill x(r,c,1) , but still x(r,c,2). it looks like one need to do something like that

    x(sub2ind(size(x),r,c,[1 1 1]))=3
    x(sub2ind(size(x),r,c,[2 2 2]))=3

I donot know how to do that once.

[ahmed shaaban]

May be something like that

for (i=1:2);x(sub2ind(size(x),r,c,[i i i]))=3;end