How Can I Append Multiple Lined Header to a CSV File?

Question

Ted Baker 2020-11-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/648988-how-can-i-append-multiple-lined-header-to-a-csv-file

评论： Peter Perkins 2020-11-18

采纳的回答： Ameer Hamza

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I am looking to create a csv file with the date/time, variable names, and a table of data - something like:

Date, 01/11/20

A, B

1, 4

2, 5

3, 7

I've created a 2x2 cell for the header, and have an array of doubles containing the data. However, I cannot understand the error message I receive when trying to use the following code. What do I need to change in the code to make this work?

savetofile = 'test.csv';
date = datetime(now,'ConvertFrom','datenum');
data = [1 4; 2 5; 3 7];
data = array2table(data);
headerlines = {'Date:', date;
                ' A', 'B'};
fid = fopen(savetofile, 'wt');
for l = 1:numel(headerlines)
    fprintf(fid,'%s\n', headerlines{l});
end
fprintf(fid, '%f; %f\n', data{:});
fclose(fid);

The error message I get is:

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not supported. Always specify a row subscript and a variable subscript, as in t(rows,vars).

What am I doing wrong the subscripting?

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Answer 1

Ameer Hamza 2020-11-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/648988-how-can-i-append-multiple-lined-header-to-a-csv-file#answer_545558

编辑：Ameer Hamza 2020-11-16

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The indexing of table using data{:} is incorrect. This shows all the ways a table can be indexed: https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html. However, writecell() will be a more robust solution.

savetofile = 'test.csv';
date = datetime(now,'ConvertFrom','datenum');
data = [1 4; 2 5; 3 7];
data = num2cell(data);
headerlines = {'Date:', date;
                ' A', 'B'};
C = [headerlines; data];
writecell(C, savetofile)

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Ameer Hamza 2020-11-16

I am glad to be of help!

Peter Perkins 2020-11-18

Ted, creating a cell array is going to use a lot of memory if your data are even moderately large, and using cell arrays for numeric adata is just a bad habit that you want to stay away from. Nothing wrong with using a table. Write your header to the file, then append to it using writetable. If you have a recent version of MATLAB, use writematrix.

Also, use date = datetime('now') instead of convert from datetime.

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