Converting Matlab .mat to csv and keeping variable names

Question

I'm trying to convert a .mat file into csv, preserving the vector/variable names. This is one example of what I'm dealing with:

mymat =

       model_id: [2217x1 double]
    own_dummies: [2217x26 double]
             id: [2217x1 double]
        product: [2217x1 double]
          const: [2217x1 double]
            mpd: [2217x1 double]
            air: [2217x1 double]
            mpg: [2217x1 double]
          trend: [2217x1 double]
          space: [2217x1 double]
           hpwt: [2217x1 double]
        cdindex: [20x1 double]
           cdid: [2217x1 double]
         outshr: [2217x1 double]
         firmid: [2217x1 double]
          share: [2217x1 double]
          price: [2217x1 double]

I've tried using csvwrite('test.csv', mymat) but it gives me an error:

??? Undefined function or method 'real' for input arguments of type 'struct'.
Error in ==> dlmwrite at 192
                str = sprintf('%.*g%+.*gi',precn,real(m(i,j)),precn,imag(m(i,j)));\
Error in ==> csvwrite at 32
dlmwrite(filename, m, ',', r, c);

I guess the problem is that I'm feeding csvwrite with a struct instead of a matrix. I can convert the struct variable to variable to a matrix, but then I would loose the variable names.

Surely there is a better way?

Where would you save the variable names then? Do you want the them to be stored in the first column? — Eitan T

Filou Filou · Accepted Answer · 2013-01-20T10:35:35

how would you actually map the struct to a csv? you cannot do a straight forward map of fieldnames as entries on first line, because the matrices have incompatible dimensions. So this example you'd have to 1. introduce several columns for own_dummies and 2. expand the cdindex.

So you could write a wrapper to make the matrices themselves compatible and to write the columns yourself into the file. something along the (untested,conceptual) lines of

    function saveData(filename, data, type)

    % at first bring struct data to sensible format
    if strcmp(type)='my_mat_type'
        data.own_dummies2 = data.own_dummies[2,:]; % split into seperate columns
        %...
        data.own_dummies26 = data.own_dummies[26,:];
        data.own_dummies = data.own_dummies[1,:];
        data.cdindex = [data.cdindex -ones(1,2217-length(data.cdindex)]; % pad any missing values as -1
    end;


    FD = fopen(filename, 'w');

    %todo did it open?

    fields = fieldnames(data);
    nfields = length(fields);

    % create column name values
    columns = strcat(strcat(fields,',')); % creates string = col1,col2,...coln,
    columns = columns(1:length(columns)-1); %remove trailing comma

    CRNL = char([10 13]); % or so

    % print columns and newline
    fprintf(FD,strcat(columns,CRNL)); 

    dataout = cell2mat(struct2cell(data));

    % use your method to write the data to the file

    fclose(FD);

naturally, you could also just split the individual fields into separate files where the fieldname is contained within the filename, which might be simpler, generally speaking.

Converting Matlab .mat to csv and keeping variable names

1 Answers