Check for existence of nested fields

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Michael Schwager
Michael Schwager on 8 Nov 2016
Commented: Stephen23 on 18 May 2020
I have a struct with some nested fields, such as cfg.accel.filename, cfg.accel.calibration, cfg.gyro.filename, etc. Sometimes the fields exist, sometimes they don't, at different levels. In the above example, the 'gyro' field could be missing, or it could just be cfg.accel.calibration that could be missing.
Is there a way to check for deeply nested fields? Currently I'm doing something like:
topstruct = struct(whatever...)
if isfield(topstruct, 'f1')
if isfield(topstruct.f1, 'f2')
if isfield(topstruct.f2, 'fleaf')
do_something(topstruct.f1.f2.fleaf)
end
end
end
Ideally I'd like to do some sort of thing like doifget(mystruct, action, field1, field2,...) where action is not actually evaluated unless mystruct.field1.field2 exists. Maybe action can be a lambda/anonymous function.
Probably just something like getif(mystruct, field1, field2, ...) returns [] if the field doesn't exist, and the value if it does.
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Accepted Answer

Thorsten
Thorsten on 10 Nov 2016
You can use my function isnestedfield:
function yn = isnestedfield(s, fields)
%ISNESTEDFIELD True if nested fields are in a structure.
% ISNESTEDFIELD(S,FIELDs) returns true if the string FIELDs is containes
% nested fields of S in the format of a single string of fieldnames
% separated by '.'
%
%Example:
% Check if s.f1.f11.f111 is a field:
% isfield(s, 'f1.f11.f111')
%
% Thorsten.Hansen@psychol.uni-giessen.de 2016-11-10
% extract fields
field = textscan(fields, '%s', 'delimiter', '.');
field = field{1};
yn = true;
structstr = 's'; % name of first input parameter
i = 1;
while yn && i <= numel(field)
% disp(['yn = isstruct(' structstr ')'])
eval(['yn = isstruct(' structstr ');']);
if yn
% disp(['yn = isfield(' structstr ', ' field{i} ')'])
eval(['yn = isfield(' structstr ', field{i});']);
end
if yn
structstr = strcat(structstr, '.', field{i});
i = i + 1;
end
end

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