Append character array to first row of a matrix

Hi there!

I've the following struct array

Astruct = 
  struct with fields:
    data1: [10×5 double]
    data2: [10×5 double]

I would like to append a column header to the values stored in the above-metnioned struct before writing to an excel sheet.

data1_header = [1,3,2,4,5];
data2_header = [1,2,3,4,10];
Astruct = 
  struct with fields:
    data1: [10×5 double]  % header 'col' + data1_header : ['col1','col3','col2','col4','col5'];
    data2: [10×5 double] %    ['col1','col2','col3','col4','col10']

Any suggestions on how to do the above will be of great help

[Stephen23]

Numeric matrices do not have headers like that.

You could use a table, which do have headers:

https://www.mathworks.com/help/matlab/tables.html

E.g. use array2table and provide those header names as a string array, then writetable.

Or you could convert the numeric data to a cell array and append the header, but that is a bit... ugly.

If the only purpose of that header is to write it to an extrernal file, then you could just call two functions:

• writecell for the header. and then
• writematrix for the numeric data.

You would need to supply appropriate cell addresses, etc.

[Deepa Maheshvare]

Thank you . Yes, the only purpose of header is to write to external file. I'm writing the struct to excel using what has been suggested here

excelFilename = 'someFile.xlsx';
structFieldnames = fieldnames(myStruct); % <--- where myStruct is your struct of data
for k = 1:length(structFieldnames)
    fieldname = structFieldnames{k};
    writematrix(myStruct.(fieldname), excelFilename, 'Sheet', sprintf('%s_matlab', fieldname));
end

`writematrix` is used to write the numeric data. I'm still trying to understand how to make use of `writecell` in the above.

I think I should simply include `writecell` prior to `writematrix`

[Deepa Maheshvare]

I tried

excelFilename = 'someFile.xlsx';
structFieldnames = fieldnames(myStruct); % <--- where myStruct is your struct of data
for k = 1:length(structFieldnames)
    fieldname = structFieldnames{k};
    writematrix(myheaderstruct.(fieldname), excelFilename, 'Sheet', sprintf('%s_matlab', fieldname));
    writematrix(myStruct.(fieldname), excelFilename, 'Sheet', sprintf('%s_matlab', fieldname), ,'WriteMode','append');
end

I get an error:

Invalid parameter name: WriteMode.

[Walter Roberson]

Writemode is new as of R2020a.

Answer 1

[Walter Roberson]

Astruct = struct('data1', randi(9,10,5), 'data2', randi(9,10,5))

data1_header = [1,3,2,4,5];
data2_header = [1,2,3,4,10];

C =  [ cellstr([ "col" + data1_header, "col" + data2_header])
      table2cell(splitvars(struct2table(V))) ];

writecell(C, excelFilename)

This assumes that you want them to go onto the same sheet. If you want different sheets then

Astruct = struct('data1', randi(9,10,5), 'data2', randi(9,10,5));

data1_header = [1,3,2,4,5];
data2_header = [1,2,3,4,10];

data_headers = {data1_header, data2_header};
data_contents = structfun(@(M) {num2cell(M)}, Astruct);

F = fieldnames(Astruct);
for K = 1 : length(F)
    C = [ cellstr("col" + data_headers{K});
          data_contents{K} ];
    writecell(C, excelFilename, 'Sheet', F{K} + "_matlab");
end

I tested, and this does create multiple sheets in the file.

What it will not do is put the data on the bottom of any existing sheet with the same name. If you want that, then you need to readcell() the existing sheet, append that at the top, and write the combination. Watch out for the possibility that the number of columns is different between the existing data and the new data.