Loop over fieldnames in a matlab structure

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David Stevens
David Stevens on 11 Aug 2015
Edited: Titus Edelhofer on 13 Aug 2015
Dears,
I have a MatLab "struct", with different "level" and "sub-structures". When printed to a cell, the data contained in the "struct", look like that:
report.COUNTRY.SOURCE.SCENARIO.CATEGORY.ENTITY = YEAR YEAR ...;
In order to produce tables listing the different variables combinations, I would like to loop over the fieldnames contained within the "struct".
I am currently trying to write a function able to do that:
fields=fieldnames(struct);
for categoryidx=1:length(fields)
categoryname=fields{categoryidx};
if isstruct(struct.(categoryname))
category=fieldnames(struct.(categoryname));
for entityidx = 1:length(category);
entityname = category{entityidx};
if isstruct(struct.(categoryname).(entityname))
gases=fieldnames(struct.(categoryname).(entityname));
end
end
end
end
Unfortunately, this is just producing anything! Does anyone has any idea how to loop over fieldnames in such a matlab structure? Thank you!

Answers (2)

Titus Edelhofer
Titus Edelhofer on 11 Aug 2015
Hi David,
generally speaking you seem to know how to loop on fieldnames ... I'm not sure now where your problem is? You can change your function to work recursively, if you don't know the number of levels, something like (note, "struct" is not an ideal variable name)
function aTable = loopovernestedstructs(aTable, aStruct)
fields = fieldnames(aStruct);
for idx = 1:length(fields)
aField = aStruct.(fields{idx});
if isstruct(aField)
aTable = loopovernestedstructs(aTable, aField);
else
% add to the table what you want, e.g., if it's a number:
aTable(end+1) = aField;
end
end
Hope this helps,
Titus
  2 Comments
Titus Edelhofer
Titus Edelhofer on 13 Aug 2015

Hi David,

maybe you can give a simple example, how it looks like, e.g.

report.USA.Reut.Scen01.Metal.Company01 = [2001 2002];
report.USA.Reut.Scen01.Metal.Company02 = [2003 2004 2005];
report.USA.Reut.Scen01.Rail.RailCompany01 = [2015];

and then how your table should look like ... ?

Then we should be able to help you out ...

Titus

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Walter Roberson
Walter Roberson on 11 Aug 2015
That appears to be me to broadly correct to me, just incomplete as it stops analyzing at gases and does not do anything with what it finds.
Have you considered using a recursive routine? Hand it a variable and the "left" information to print out. If it detects the variable is a struct, iterate over its fields, passing the field content and the "left" information and the field name recursively into the routine. If it detects that it is working with a non-struct, print or return a report on the content.
  1 Comment
David Stevens
David Stevens on 12 Aug 2015
Hi, Thank you for your answer. It´s not really necessary for me to do a recursive routine as I already know the number of structure level (5). As you suggested, I would like to print the results in a table. For this table I would like to have the level 4 of the structure as the column header and the number 5 of the structure as the row header. Then the table shall be filled with the existing combination results between level 5 and 4. Do you have any idea about how to achieve that?

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