Accessing various field names deep in a structure.

hi

Image I want to access fieldnames one, two, three, four in structure A.B.C.D.E.F and so on, with each possible letter containing fieldnames one, two, three four, e.g. A.B.C.one, A.B.C.two. In one iteration, I might wanna get A.B.C.one, but in the next A.B.C.D.one. I could of course make switch cases like: case condition, then go to A.B.C.D.one, case ..., but I would like to parse to common part of the fieldnames, e.g. 'B.C.D.E' to A. like this: A.('B.C.D.E').one. As such, ('B.C.D.E') could be easily replaced by e.g. ('B.C.') and my code would be less redundant. In a post by Loren, I found the answer below to solve my problem, posted by Brad Stiritz. However, I don't get this to work, when I try

A.B.C.D = 50; ans = A.getField('A.B.C.D')

I get

Reference to non-existent field 'getField'.

I tried ans = getField(A,'B.C.D') and ans = getField(A,'A.B.C.D'), but also got errors. Anyone who has a similar solution or can get this to work?

Thx!

I cite: " I wrote a class ‘FieldInterface’ to encapsulate arbitrary-depth struct fields, just as you’re talking about, so I can do things like:

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A.setField(‘A.B.C.D’,20); ans = A.getField(‘A.B.C.D’);

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The code snip below is the essence of method getField(). Note the reference to classdef constant ROOT_FIELD_NAME, which anchors the “dynamic” Fields.

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function outValue = getField(obj,varargin) … fieldSpecStr = varargin{1}; … try

% Construct near-complete field name (only lacking ‘obj.’), e.g. % ‘ROOT_FIELD_NAME.subStructName.fieldName’ fullFieldStr = [ obj.ROOT_FIELD_NAME '.' fieldSpecStr ];

% Get cell vector of sub-struct / field names within (fullFieldStr) cvFieldSplits = regexp(fullFieldStr,’\.’,'split’);

% Initialize (outValue): outValue = obj;

% Iterate through (cvFieldSplits) for iSplit = 1 : numel(cvFieldSplits)

% Access next-level within (cvFieldSplits), which will either be a % further sub-struct or else the final, desired field: outValue = outValue.(cvFieldSplits{iSplit}); end

% Handle failure catch exception … end

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Hope s/o finds this useful. Any comments appreciated,

Brad " from: http://blogs.mathworks.com/loren/2005/12/13/use-dynamic-field-references/

[babi psylon]

O, I get it, A is an object, and setField like something you apply to this object. I'm not familiar with object oriented programming. Any change I might get this to work though?

[Azzi Abdelmalek]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Matt J]

It just seems like a bad idea to nest structs so deep. Most of the indexing you describe is basically what struct arrays were designed for. So, rather than having

 one.two.three.two.one.F

you would instead make F a struct array and do F(1,2,3,2,1).

Answer 1

[babi psylon]

A solution seems to be posted here: http://stackoverflow.com/questions/3753642/how-can-i-dynamically-access-a-field-of-a-field-of-a-structure-in-matlab

Answer 2

[Paul Jordan]

A.B.C.D = 50;
s = {'B','C','D'};
getfield(A,s{:})

ans =

    50

[Cristian Constantinescu]

This is such a concise and elegant solution to something I've been searching for a while.

Thank you!