writetable Matlab (appendtable?)

Question

If you have a table class "T"

T =

Var1      Var2      Var3    Var4 
____    ________    ____    _____

M       45    45    'NY'    true 
F       41    32    'CA'    false
M       40    34    'MA'    false

And you want to write the values in a file you could use, for instance:

writetable(T,'myData.txt','Delimiter', ...)

But this will delete all the information you had in myData.txt . I was wondering if there is an append function for table, or some way write without remove the old content of myData.txt.

So, Image:

type myData.txt

Hello

writetable(T, ...)

type myData.txt

Hello

Var1 Var2 Var3 Var4

M       45    45    'NY'    true 
F       41    32    'CA'    false
M       40    34    'MA'    false

score 2 · Accepted Answer · answered Jan 20 '15 at 12:53

One way is to write to the file using fopen(). Create the table:

LastName = {'Smith';'Johnson';'Williams';'Jones';'Brown'};
Age = [38;43;38;40;49];
Height = [71;69;64;67;64];
Weight = [176;163;131;133;119];
T = table(LastName,Age,Height,Weight)

Write the file:

writetable(T,'table.csv')

Open the file again:

fid = fopen('table.csv','a')

Write out the table a second time:

fmt = varfun(@(x) class(x),T,'OutputFormat','cell');
fmt(strcmp(fmt,'double'))={'%g'};
fmt(strcmp(fmt,'cell'))={'%s'};
fmt=[strjoin(fmt,',') '\n']
for r=1:size(T,1)
  x=table2cell(T(r,:));
  fprintf(fid,fmt,x{:});
end
fclose(fid);

Which is a polite way of saying `writetable` is brain-dead so you have to go the hard way. Plenty other languages have a similar function with an argument `append` that can be set to TRUE for exactly this purpose. — Carl Witthoft, Jan 28 '21 at 19:06

score 2 · Answer 2 · answered Oct 14 '16 at 09:34

Bob's answer is perfect for small tables. For large tables, to avoid the for loop, I recommend writing the second table to a second file, and then you can merge the files. Here is code for that:

writetable(T1,'data_01.csv');
writetable(T2,'data_02.csv','WriteVariableNames',false);

you don't want to have the variable names on the second file so that you can merge the files perfectly to a new file. If you are on Linux you can simply do:

cat data_*.csv >> data.csv

And, yet if the tables are very big, I would recommend using 'datastore'. Here is a code for that:

writetable(T1,'data_01.csv');
writetable(T2,'data_02.csv');

here we should keep the variableNames in the second file as well, so the datastore function can read the files properly:

ds = datastore('data_*.csv');

then, you can read slice by slice using 'read' function or read completely using 'readall' function, depending on your need. Please, check the documentations for that.

And for windows, you can use: system(['type ' FileNames{n} ' >> ' Ofilestr]); Source: https://stackoverflow.com/questions/32710933/matlab-combining-text-files — M.Hossein Rahimi, Jan 21 '20 at 14:26

writetable Matlab (appendtable?)

2 Answers2