Using 'union' function in a loop over fieldnames

Dears,

I Have a MatLab structure (see enclosed) I am running a loop over the fieldnames of this structure. This structure is composed as follow : COUNTRY.SOURCE.SCENARIO.CATEGORY.ENTITY. At one point I would like to compare the ENTITY linked with each CATEGORY using the 'union' function, and then output just a value of gases entails in all the CATEGORY together. I am currently using the following function.

 function comboloop = loopoverV2(myStruct)
country = fieldnames(myStruct)
for countryidx = 1:length(country)
    countryname = country{countryidx}
    source = fieldnames(myStruct.(countryname))

    for sourceidx = 1:length(source)
        sourcename = source{sourceidx};
        scenario = fieldnames(myStruct.(countryname).(sourcename))

        for scenarioidx = 1:length(scenario)
            scenarioname = scenario{scenarioidx};
            category_full = fieldnames(myStruct.(countryname).(sourcename).(scenarioname));
            category = intersect(category_full,category_header)
            allGas = [];

            for categoryidx = 1:length(category)
                categoryname = category{categoryidx};
                gas_full = fieldnames(myStruct.(countryname).(sourcename).(scenarioname).(categoryname))               
                gas = union(allGas,gas_full)
            end
        end
    end
end

Unfortunately this is not working as I expected. Does anyone as any idea why? Thank you so much!

Answer 1

[Titus Edelhofer]

Hi,

what do you mean by "not working as expected". Does it throw an error? Wrong result? Nothing happens?

One thing that you should change in any case is the initialization of allGas: since the fieldnames below are a cell array of strings, allGas should be an empty cell:

allGas = {};

Titus

[Titus Edelhofer]

BTW, the structure looks as if I've seen it before :).

[David Stevens]

Hi,

In fact in the current state of the function, the union function just don´t combine any values. Inside the loop of my function, each 'category' return some 'gas_full'. My wish is that at the end the union function combined all results from the combination "category"."gas_full" in just one cell array. Currently it just return for each 'category' a cell array with the entails 'gases'. (My query might look unclear, I am really sorry about that, I keep trying to clarify that even in my head!).

Best regards, David

p.s: You already helped me few weeks ago on that exact same function ;)

[Titus Edelhofer]

Hi David,

if you have this code:

allGas = {};
for categoryidx = 1:length(category)
   categoryname = category{categoryidx};
   gas_full = fieldnames(myStruct.(countryname).(sourcename).(scenarioname).(categoryname));
   allGas = union(allGas,gas_full);
end

Then after the loop the variable allGas should contain a list of names, i.e., one cell array...?

But if in each category you want to store more than just the names of the gases you would need to do something different, more like

allGas = {};
for categoryidx = 1:length(category)
   categoryname = category{categoryidx};
   gas_full = struct2cell(myStruct.(countryname).(sourcename).(scenarioname).(categoryname));
   allGas(end+1,:) = gas_full';
end

Maybe you can show us, what myStruct.(countryname).(sourcename).(scenarioname).(categoryname) looks like for one or two categories, and then what allGas should look like...? Titus