How to brows variable names of a structure and select the closest to a given string?

Hi there,

I imported motion capture data to Matlab in the form of a structure.

e.g. Experiment1 file:

data.head_12.time; data.head_12.data

data.arm_4.time; data.arm_4.data

...

Sometimes the index allocated to the marker sets changes between experiments, which results in a change of the variable name in the structure:

e.g. Experiment2 file:

data.head_16.time; data.head_16.data

data.arm_11.time; data.arm_11.data

...

How can I select the closest variable name without knowing the index?

myvariable = find(data.filednames, 'head_xx').data;

[Stephen23]

A much better way to design your data would be to NOT force meta-data into the fieldnames.

For example:

data.head.meta = 12;
data.head.time = ..
data.head.data = ..
data.arm.meta = 4;
data.arm.time = ..
data.arm.data = ..

Then you can simply match the field's value, which would be 100 times easier (as well as simpler, more robust, more efficient) than what you are going to end up doing:

https://www.mathworks.com/matlabcentral/answers/225435-save-variable-as-string-from-user-input#answer_184104

Or even generalize your data into a flattened structure array:

data(1).type = "head";
data(1).meta = 12;
data(1).time = ..
data(1).data = ..
data(2).type = "arm";
data(2).meta = 4;
data(2).time = ..
data(2).data = ..

which gives you lots of flexibility and easy of data access:

https://www.mathworks.com/matlabcentral/discussions/tips/847976-tutorial-comma-separated-lists-and-how-to-use-them

Meta-data is data, and forcing it into fieldnames (or worse, variable names) makes your data harder to process.

[M.B]

I understand your point. Unfortunately, I have no control over the naming of variables, which is done in the MOCAP software.

[Image Analyst]

If you have any more questions, then attach your data files and code to read it in with the paperclip icon after you read this:

TUTORIAL: How to ask a question (on Answers) and get a fast answer

Answer 1

[Sameer]

Hi

To select the closest variable name without knowing the exact index, you can use "dynamic field names" and "regular expressions" to match the desired pattern.

Here's how you can do this:

1. Use "fieldnames()" to get all field names from the structure.

2. Use "regexp()" to find the field name that matches your pattern.

3. Access the data using dynamic field names.

Sample Code :

data.head_12.time = 0:0.1:10; % Sample time data
data.head_12.data = sin(data.head_12.time); % Sample data

data.arm_4.time = 0:0.1:10; % Sample time data
data.arm_4.data = cos(data.arm_4.time); % Sample data

data.leg_7.time = 0:0.1:10; % Sample time data
data.leg_7.data = tan(data.leg_7.time); % Sample data

% Now, let's find the field that matches 'head_xx'
fields = fieldnames(data);
pattern = '^head_\d+$'; % Pattern to match 'head_' followed by digits

matches = regexp(fields, pattern, 'match');
matchedField = fields(~cellfun('isempty', matches));

if ~isempty(matchedField)
    selectedField = matchedField{1};
    myTime = data.(selectedField).time;
    myData = data.(selectedField).data;
    disp(['Selected field: ', selectedField]);
    disp('Time data:');
    disp(myTime);
else
    error('No matching field found for pattern: %s', pattern);
end

Selected field: head_12

Time data:

  Columns 1 through 18

         0    0.1000    0.2000    0.3000    0.4000    0.5000    0.6000    0.7000    0.8000    0.9000    1.0000    1.1000    1.2000    1.3000    1.4000    1.5000    1.6000    1.7000

  Columns 19 through 36

    1.8000    1.9000    2.0000    2.1000    2.2000    2.3000    2.4000    2.5000    2.6000    2.7000    2.8000    2.9000    3.0000    3.1000    3.2000    3.3000    3.4000    3.5000

  Columns 37 through 54

    3.6000    3.7000    3.8000    3.9000    4.0000    4.1000    4.2000    4.3000    4.4000    4.5000    4.6000    4.7000    4.8000    4.9000    5.0000    5.1000    5.2000    5.3000

  Columns 55 through 72

    5.4000    5.5000    5.6000    5.7000    5.8000    5.9000    6.0000    6.1000    6.2000    6.3000    6.4000    6.5000    6.6000    6.7000    6.8000    6.9000    7.0000    7.1000

  Columns 73 through 90

    7.2000    7.3000    7.4000    7.5000    7.6000    7.7000    7.8000    7.9000    8.0000    8.1000    8.2000    8.3000    8.4000    8.5000    8.6000    8.7000    8.8000    8.9000

  Columns 91 through 101

    9.0000    9.1000    9.2000    9.3000    9.4000    9.5000    9.6000    9.7000    9.8000    9.9000   10.0000

Please refer to the below MathWorks documentation links:

https://www.mathworks.com/help/releases/R2020a/matlab/ref/fieldnames.html

https://www.mathworks.com/help/releases/R2020a/matlab/ref/regexp.html

Hope this helps!

[M.B]

Thanks Sameer.

I will give it a try and report back.

[M.B]

It did work with a small tweek.

The variable names were a bit more complex than the simple example I provided.

E.g.

data.head_12_x.time

data.head_12_y.time ...

I searched for the follwoing match "head_" because the I only have one head and the sufix after the index is always in this order: x y z r p w. So I know that the first match is X etc.