Question

How can I use the function FIND to count the number of items of a given value instead of using a loop? For example, in the array item below there are 3 occurrences of the number 23, 2 occurrences of the number 22, and 2 occurrences of the number 20.

....
for i=2:n
    if item(i-1)~=item(i)
        nItem21(i)=1;
    else 
        nItem21(i)=nItem21(i-1)+1;
    end
end

item Num
23   2
23   4
23   6
22   3
22   1
20   6
20   8

Answer 1

You can do the following: identify where the value of item changes, then use diff to get the counts.

item = [
23   
23   
23   
22   
22   
20   
20];

% find the 'last' entries of each consecutive group of numbers
chgRowNum = [find(item(1:end-1) ~= item(2:end);length(item)]; 

counts = diff([0;chgRowNum]);

correspondingItems = item(chgRowNum);