Check for existence of nested fields

Question

Michael Schwager 2016-11-8

2
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311264-check-for-existence-of-nested-fields

评论： Stephen23 2020-5-18

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.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Michael Schwager 2016-11-11

I think that would probably work, but I guess using try/catch for non-errors is something I come to understand as a questionable practice. I can try it and see how the code ends up looking.

Stephen23 2020-5-18

See:

https://www.mathworks.com/matlabcentral/answers/95923-is-there-a-matlab-function-that-can-check-if-a-field-exists-in-a-matlab-structure#answer_105275

https://www.mathworks.com/matlabcentral/answers/94122-is-there-a-function-that-will-display-all-the-fields-of-a-nested-structure-in-matlab#answer_103473

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Thorsten 2016-11-10

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/311264-check-for-existence-of-nested-fields#answer_242768

在 MATLAB Online 中打开

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