"Im still quite new to MatLab and have spent almost the whole day to no avail in figuring this out"
Storing numeric data in a cell array makes your life much harder. So the first thing to do is to put all of the numeric data into numeric arrays, then the solution is quite easy using ismember and some simple indexing.
C = {...
1 '200' NaN
2 '100' NaN
3 '200' NaN
4 '200' 1
5 '100' 2
6 '100' 3
7 '200' 4
8 '200' 5
9 '200' 6
10 '100' 7
11 '100' 8
12 '100' 9};
>> obj = vertcat(C{:,1}); % first column -> numeric
>> ref = vertcat(C{:,3}); % third column -> numeric
>> [idx,sub] = ismember(ref,obj); % match values in the two columns
>> idz = strcmp(C(:,2),'200'); % identify '200'
>> out = idx;
>> out(idx) = idz(idx) & idz(sub(idx))
out =
0
0
0
1
0
0
1
0
0
0
0
0
this returns a logical index, which is often more efficient to use than subscript indexing. If you really need to get the subscript indexing then just use find:
>> find(out)
ans =
4
7
>>
