Assigning 0 if a variable is not present in mat file

I am trying to assign zero to a variable which is not available in mat file. I am trying to make it work with following code which is not working as per my logic.

variables= {'abc','def','ghi','jkl','mno'};
data= load('xyz.mat')
 
 
        for pr=1:numel(variables)
            if isfield(data, variables(pr))==0
                variables(pr)=zeros(1,100);
            end
        end
 

I am not able to make it work like I want to. So basically what I am trying to do is if suppose variable abc is not there in xyz.mat, I want to create abc of zeros(1,100) and if def is there in xyz.mat then I want to use it as it is.

Is this possible in matlab?

[Stephen23]

https://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

Answer 1

[Walter Roberson]

            if ~isfield(data, variables{pr})
                data.(variables{pr}) = zeros(1,100);
            end

Now extract everything from data

[adi kul]

I am facing issue while doing this over the loop.

variables= {'abc','def','ghi','jkl','mno'};

for i=1:10
    data(i)=load([folder,file],variables{:})
    for pr=1:numel(variables)
        if ~isfield(data, variables{pr})
                data(i).(variables{pr}) = zeros(1,100);
        end
    end
end

With this data will have values from last mat file only while with following code, it will have 10 rows of data if same variables are present in all the mat files

variables= {'abc','def','ghi','jkl','mno'};

for i=1:10
    data(i)=load([folder,file],variables{:};
end

The problm with above piece of code is, if 1st mat file have all the 5 variables in it and in 2nd mat file if there are only 3 then the code either throws error or if I use try-catch then the data will have only 1 matfile data. even though it goes through all the 10 files, final data witll be 1x1 struct type.

[Walter Roberson]

variables= {'abc','def','ghi','jkl','mno'};
for i=1:10
    data{i}=load([folder,file],variables{:})
    for pr=1:numel(variables)
        if ~isfield(data{i}, variables{pr})
                data{i}.(variables{pr}) = zeros(1,100);
        end
    end
    data{i} = orderfields(data{i});
end
data = [data{:}];

[adi kul]

now with this I am facing issue to concatenate.

So I am taking the output of data function to another script where I concatenate all the rows of the data. User will define the Parameters and from data created by above function will be processed.

Getting this error:

Error using vertcat
Dimensions of matrices being concatenated are not
consistent.

This is the code:

Parameters= {'abc','def'}
for ii=1:numel(Parameters)
    
    jj=char(Parameters(ii));
    if isfield(data,jj)==1
        value=vertcat(data.(jj));
        assignin('base',jj,value);
    continue;
    end
  
end

[Walter Roberson]

The vertcat() is not doing anything useful for you. You are only passing in a single parameter, and a parameter concatenated with nothing is the same as the parameter.

assignin('base') is recommended against; it has most of the same problems that using global has.

[Walter Roberson]

I did recognize a difficulty with the

data = [data{:}];

at the time I posted it. The loop checking for those variables ensures that at least those variables are present, but it does not do anything about the possibility that additional variables are present in a file. The concatenation of structures that I do can only work if all of the struct have the same fields in the same order; the orderfields() call imposes a consistent order of the fields that are present, but the logic I posted does not protect against the possibility that some file has extra fields; your problem statement does not define what the result should be in that case.