Question

I have an array of structs where I perform two searches. First I search for a specific colour and then I search for a specific city. I get two data sets containing the data I was looking for. So far, no problems.

From the two data sets I get, I would like to find the structs in the two data sets that are present in both data sets.

I have tried ‘intersect’, as this seemed to be a good option for arrays. But I do not seem not get any intersected data… Why not?

The code looks something like this:

%Array of structs
InfoArray(1) = struct  ('Name','AAAA', 'City', 'London', 'Test', '70', 'FavouriteColor', 'red');          
InfoArray(2)= struct('Name','BBBB', 'City', 'London', 'Test', '20', 'FavouriteColor', 'blue');        
InfoArray(3)= struct('Name','CC', 'City', 'London', 'Test', '10', 'FavouriteColor', 'white');        
InfoArray(4)= struct('Name','DD', 'City', 'Stockholm', 'Test', '30', 'FavouriteColor', 'yellow');          
InfoArray(5)= struct('Name','EEEEE', 'City', 'Oslo', 'Test', '15', 'FavouriteColor', 'red');     
InfoArray(6)= struct('Name','FFFF', 'City', 'Oslo', 'Test', '15', 'FavouriteColor', 'red');      
InfoArray(7)= struct('Name','GG', 'City', 'Stockholm', 'Test', '80', 'FavouriteColor', 'blue');           
InfoArray(8)= struct('Name','H', 'City', 'Oslo', 'Test', '60', 'FavouriteColor', 'pink');       
InfoArray(9)= struct('Name','III', 'City', 'Oslo', 'Test', '5', 'FavouriteColor', 'red');      
InfoArray(10)= struct('Name','JJJJ', 'City', 'Stockholm', 'Test', '40', 'FavouriteColor', 'blue');   
InfoArray(11)= struct('Name','KKKK', 'City', 'London', 'Test', '70', 'FavouriteColor', 'white');       




%Find structs in array with color: 'red'

iColor = 'red';
[pFound,matchingFavouriteColors] = findPost(InfoArray,'FavouriteColor',iColor);

%Find structs in array with City: 'London'

iCity = 'London';
[pFound,matchingCity] = findPost(InfoArray,'City',iCity);

%Find the structs that are found in both of the data sets ????
[c, ia, ib] = intersect(matchingFavouriteColors, matchingCity);
disp([c; ia; ib]) 



function [matchFound, matchingData] = findPost(db,sField,iField)
    matches = find(strcmpi({db.(sField)},iField));
    if(isempty(matches))
        disp('No matches found');
        postsFound=0;
    else
        matchingData = db(matches(:));
        matchFound=length(matches);
    end

Answer 1

What error message does intersect give you? That should give you a hint why it does not work.

To accomplish what you want, you do not need your findPost function (which has an assignment that does nothing at postsFound=0; and a misleadingly named variable matchFound, btw.), you can use logical indexing.

iRed = strcmpi({InfoArray.FavouriteColor},'red');
iLondon = strcmpi({InfoArray.City},'London');
InfoArray(iRed & iLondon)

iRed contains 1s exactly where the color is red, iLondon at the indices where the city is london, and iRed & iLondon exactly where both are true — and these logical arrays can be used as index to your struct array.

Edit: Alternatively, you could get hold of the numeric indices (i.e. the results of find(strcmpi({db.(sField)},iField)) and use intersect on them, getting the numeric indices to the array elements you want, but this seems a bit … indirect.