How to writetable to file with 2nd row containing VariableUnits?

Hi Everyone,

I would like to know how to write a table to file including the metadata (specifically VariableUnits). the function " writetable " does not seem to allow for this function. I have tried to writ table to a comma delimited file and use dlmwrite (....'-append') but this adds the unit row at the bottom of the file and one character at the time instead of the entire string. I would like to have it in the 2nd row, right underneath the variable names.

[Jan Kappen]

Are there any non-verbose solutions using writetable available? We should really be able to choose to export variable units (e.g. by appending them to the variable name in brackets or parentheses).

[Voss]

t = table([1;2;3],[4;5;6]);
t.Properties.VariableNames = {'A','B'};
t.Properties.VariableUnits = {'m','ft'};

filename = 'file.txt';
writetable_with_units_line(t,filename)
type(filename)

A,B
m,ft
1,4
2,5
3,6

writetable_with_units_in_brackets(t,filename)
type(filename)

A[m],B[ft]
1,4
2,5
3,6

function writetable_with_units_line(t,filename)
fid = fopen(filename,'w');
str1 = strjoin(t.Properties.VariableNames,',');
str2 = strjoin(t.Properties.VariableUnits,',');
fprintf(fid,'%s\n%s',str1,str2);
fclose(fid);
writetable(t,filename,'WriteMode','append','WriteVariableNames',false,'Delimiter',',');
end


function writetable_with_units_in_brackets(t,filename)
fid = fopen(filename,'w');
str = strjoin(t.Properties.VariableNames+"["+t.Properties.VariableUnits+"]",',');
fprintf(fid,'%s',str);
fclose(fid);
writetable(t,filename,'WriteMode','append','WriteVariableNames',false,'Delimiter',',');
end

[Jan Kappen]

Thanks for that proposal. Yeah it can be done this way, but I'd prefer not to write my own function for that ;)

BTW, I think you can make it shorter without using fopen and friends...

function writetable_with_units_in_brackets(T, filename)
    arguments
        T table
        filename (1,1) string
    end
    
    namesWithUnits = T.Properties.VariableNames + " (" + T.Properties.VariableUnits + ")";
    T.Properties.VariableNames = namesWithUnits;
    
    writetable(T, filename, Delimiter=",");
end

But again - no function would be better.

A solution could be an extended version of the table class, adding a property WriteVariableUnits which gets parsed during writetable. But since table can't be subclassed that will never happen :(

Answer 1

[Miguel Aznar]

I found a work around it. It is pretty simple. I hope it helps whoever is stuck trying to do the same. Write first the header with fprinf indicating %s as the formatting of your cell array. Do not forgwt the break in the last cell "\n", and indicate the metadata of your table (i.e. Table.Properties.VariableNames {1,1:end})

fid = fopen('test.csv','w')
fprintf('test.csv', '%s, %s, %s, %s, %s, %s\n', Table.Properties.VariableNames{1,1:end});
fprintf('test.csv', '%s, %s, %s, %s, %s, %s\n', Table.Properties.VariableUnits{1,1:end});
M = table2array(Table);
dlmwrite('test.csv', M, '-append') ;