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Checking if a nested field exists in a structure

16 Ansichten (letzte 30 Tage)
KAE am 28 Apr. 2020
Bearbeitet: KAE am 15 Mai 2020
I am building a structure whose fields and subfields are nested structures. I would like to cycle through a subfield, determine if any values have been assigned yet, and if not, assign a value to the end of an array. Here is an example in which I am checking how many potato dishes guests are bringing to a potluck Thanksgiving dinner. Is there a better way to do this? My real dataset has many more fields than this example.
potatoList = {'Yam', 'White', 'Candied'};
for iPerson = 1:4 % cycle through guests
for iPotato = 1:length(potatoList)
isFirst = false; % Is this the first entry for a given type of potato or not?
if ~exist('Thanksgiving', 'var') % Haven't even created the structure yet
isFirst = true;
else % Structure exists, but subfield may not
if ~isfield(Thanksgiving, 'Potato')
isFirst = true;
if ~isfield(Thanksgiving.Potato, potatoList{iPotato})
isFirst = true;
if isFirst
iValue = 1; % The first time, the index starts at one
% Placeholder for nested subfield before value is assigned, to avoid
% error due to field not existing yet
Thanksgiving.Potato.(potatoList{iPotato}).number = [];
% After the first time, the index starts at the end of the array
iValue = length(Thanksgiving.Potato.(potatoList{iPotato}).number) + 1;
% Assign example values to array
Thanksgiving.Potato.(potatoList{iPotato}).number(iValue) = ...
round(rand(1)*10); % Number of potato dishes someone is bringing

Antworten (1)

rajat aggarwal
rajat aggarwal am 13 Mai 2020
You can use indexing to access the fields of data structure. Some people have also developed some API for accessing data structure in MATLAB.
You can also generate field names from variables. Please refer to following link for more information.
It is not clear from code that what fields and data fields are present in your potato structure. If you need more inputs on this, Please share your structure details.
  1 Kommentar
KAE am 14 Mai 2020
Bearbeitet: KAE am 15 Mai 2020
You should be able to run the code I provided to generate an example structure with many nested fields. In the code, I have to check if a subfield does not exist yet (isFirst = true) and assign an empty placeholder value [] before assigning numerical values. I am wondering if there is a better way.
If my question is still unclear please let me know.

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