creating new fields in multiple structures with loops
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Manthos Vogiatzoglou
el 16 de Mzo. de 2020
Editada: Ameer Hamza
el 17 de Mzo. de 2020
Hi all
I have some data in the form of structures, eg strA, strB e.t.c. All structures have the same fields, let's say f1 and f2. I want to create the same new fields in every structure, for example:
strA.mean = mean(strA.f1);
strA.std = std(strA.f1);
Is there a way to do this with a loop so I don't have to write the above two lines of code for each structure? I tried the following but it doesn't work:
structnames = {'strA','strB','strC','strD','strF','strG','strK'}
n = length(structnames)
for i = 1:n
structnames{i}.mean = mean(structnames{i}.f1);
structnames{i}.std = std(structnames{i}.f1);
end
Any ideas?
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Ameer Hamza
el 16 de Mzo. de 2020
It is never a good idea to name your variables like strA, strB, strC, ... There is a done of discussion on this topic explaining why it is an inefficient and dangerous: https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval. A better strategy is to create an array of struct accessible as str(1), str(2), str(3), ...
Although it is possible to do what you asked in your question, I will not be a part of this sin ?and only show you a way to create a struct array. After that, you can easily add a new field to all the fields to all the elements of the array.
strA.f1 = rand(1,10);
strA.f2 = rand(1,10);
strB.f1 = rand(1,10);
strB.f2 = rand(1,10);
% create the array of struct
clear str
vars = whos('str*');
str(numel(vars)) = struct('f1', [], 'f2', []);
for i=1:numel(vars)
str(i) = eval(vars(i).name);
end
% see how easy it is now
for i=1:numel(str)
str(i).mean = mean(str(i).f1);
str(i).var = var(str(i).f1);
end
3 comentarios
Ameer Hamza
el 17 de Mzo. de 2020
It that case, it is still a better strategy to create struct arrays and save the name of the animals as a field of each struct. For example, try this.
lions.sex = {'M','M','F','F','F','M','F','F','M','F','F','F','M'};
lions.region = [1,1,1,1,1,1,2,2,2,2,2,2,3];
tigers.sex = {'F','M','F','M','F','M','F','F','F','M','F','M','F'};
tigers.region = [1,2,2,3,3,1,2,2,2,2,2,2,1];
% create the array of struct
vars = {'lions', 'tigers'};
clear animals
for i=1:numel(vars)
animals(i) = eval(vars{i});
end
% see how easy it is now
for i=1:numel(animals(i))
animals(i).name = vars{i};
animals(i).mean = mean(animals(i).region);
animals(i).var = var(animals(i).region);
end
Ameer Hamza
el 17 de Mzo. de 2020
Editada: Ameer Hamza
el 17 de Mzo. de 2020
Now in case, it is absolutely necessary to keep the names of variables, and you have no other choice, then you can try this.
lions.sex = {'M','M','F','F','F','M','F','F','M','F','F','F','M'};
lions.region = [1,1,1,1,1,1,2,2,2,2,2,2,3];
tigers.sex = {'F','M','F','M','F','M','F','F','F','M','F','M','F'};
tigers.region = [1,2,2,3,3,1,2,2,2,2,2,2,1];
structnames = {'lions', 'tigers'};
for i=1:numel(structnames)
% create the actual command as a string
eval([structnames{i} '.mean = mean(' structnames{i} '.region);']);
eval([structnames{i} '.var = var(' structnames{i} '.region);']);
end
This will keep the variables names the same as before and add new fields, as shown inside the eval() function.
Más respuestas (1)
Fangjun Jiang
el 16 de Mzo. de 2020
Editada: Fangjun Jiang
el 16 de Mzo. de 2020
This is the time to use structure array, not to use strA, strB, strC, ...
Just like use array A=1:3, not to use A1=1, A2=2, A3=3.
If you had strA, strB, strC, etc. from somewhere else, then you could do
str=[strA;strB;strC] and follow the code by @Ameer Hamza
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