How to acces a variable in structure when i only have the string saved into a variable

Question

Adrien 2014-8-28

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152623-how-to-acces-a-variable-in-structure-when-i-only-have-the-string-saved-into-a-variable

回答： Jos (10584) 2014-8-28

采纳的回答： Jos (10584)

在 MATLAB Online 中打开

Hello,

Here is my code :

[filename, pathname] = uigetfile('*.mat', 'Select the MATLAB mat file');
a = load(filename);

I'm asking a file to the user. And then loading the array of the coresponding file into a. But it is saved as a Structure. a is a Structure that contained a variable named by the name of the filename. Which is itself containing the array. Am I right ? After that I want to plot it.

plot(a.??);

The problem is, that i can't right a.filename. Cause filename is not the real name, but the name of the varaible that contain the string I want.

I hope you'll understand my problem.

Thank you in advance.

2 个评论
显示无隐藏无

Adam 2014-8-28

Are you expecting the user to have saved a specifically named variable in their .mat file?

Otherwise there could be any number of variables being loaded in when you load the file.

Adrien 2014-8-28

在 MATLAB Online 中打开

Yes. Is the mat file not like a structure ? You can save for example :

a = load ('****.mat')

Than :

a = 
     aaa: [1x100 double]
     bbb: [1x100 double]

How can i access for example aaa without knowing aaa. But only the name of the file and the position into the file. I mean aaa is now 1.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Jos (10584) 2014-8-28

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152623-how-to-acces-a-variable-in-structure-when-i-only-have-the-string-saved-into-a-variable#answer_150072

在 MATLAB Online 中打开

This would be an approach

[filename, pathname] = uigetfile('*.mat', 'Select the MATLAB mat file');
tmp = load(filename);
fn = fieldnames(tmp) ; 
X = tmp.(fn{1}) ; % simply take the first (and may be only) variable)
plot(X)  % use X in the remainder of the code

or if you know that you want to load a specific variable from the matlfile

tmp = load(filename)
varname = 'MyDataVar' ;
if ~isfield(tmp, varname)
  error('The file %s does not contain the variable "%s",filename, varname)
else
  X = tmp.(varname) ;
end