How can I write a table from a matrix?

Question

Szabó-Takács Beáta 2017-7-26

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https://ww2.mathworks.cn/matlabcentral/answers/350282-how-can-i-write-a-table-from-a-matrix

回答： Peter Perkins 2017-7-26

Dear All, I have a matrix pr(10958,30888) and three vectors year(10958,1), month(10958,1) and day(10958,1). I would like to create a table(10958,30892) from these. I tried the following way:

for i=1:30888
P=table(year,month,day,pr(:,i));
end

but it created a table what had only 4 column (year,month,day,var1). Can someone suggest me a solution? Thank you for your help in advance!

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Andrei Bobrov 2017-7-26

Hi Beáta!

Please attach small part of the your data.

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Answer 1

Walter Roberson 2017-7-26

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https://ww2.mathworks.cn/matlabcentral/answers/350282-how-can-i-write-a-table-from-a-matrix#answer_275554

在 MATLAB Online 中打开

   t = array2table([year, month, day, pr]);
   t.Properties.VariableNames(1:3) = {'year','month','day'};
   t.Properties.VariableNames(4:end) = cellstr(num2str((1:size(pr,2))','pr%d'));

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Guillaume 2017-7-26

编辑：Guillaume 2017-7-26

You have been given two quick processes.

It creates t(10958,30891) table

So you have the table you wanted

I do not find the data

Sorry, we can't read your mind or see what you're doing. You're obviously doing something wrong or do need to learn to use matlab.

I have to write the data in table to .txt file.

Have you tried writetable ?

P=join(P1,P2)

Reading the documentation is a must. join does not just sticks two tables side by side. (that is achieved by the concatenation operator []) and is certainly not the solution you are looking for. For that matter, the documentation has plenty of examples on how to create tables. None of them use loops for that.

Walter Roberson 2017-7-26

在 MATLAB Online 中打开

summary(t) to get an overview of it; https://www.mathworks.com/help/matlab/ref/summary.html

Extract parts of it to view it, such as

t{1:2,1:10}

to see the first two rows and first 10 columns

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Answer 2

Andrei Bobrov 2017-7-26

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https://ww2.mathworks.cn/matlabcentral/answers/350282-how-can-i-write-a-table-from-a-matrix#answer_275551

在 MATLAB Online 中打开

c = num2cell(pr,1);
TTout = timetable(datetime(year1,month1,day1),c{:});

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Szabó-Takács Beáta 2017-7-26

Dear Andrei, I attached a small part from my data. I tried your suggestion above, but unfortunately it does not work.

Guillaume 2017-7-26

"unfortunately it does not work"

There may be many reason for why it doesn't work. One of them could be that you're on an older version of matlab which does not have timetable.

Rather than letting us guess, give us the error message or the reason why it does not work. It does not work is totally unhelpful.

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Answer 3

Peter Perkins 2017-7-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/350282-how-can-i-write-a-table-from-a-matrix#answer_275612

在 MATLAB Online 中打开

Perhaps the most straight-forward thing to use to get a table with 30891(=30888+3) variables in it would be

t = [table(year,month,day) array2table(pr)]

but I would question the usefulness of a table with that many variables. It works, but is it useful?

What about

t = table(year,month,day,pr)

which creates a table with four variables, one of which itself has 30888 columns.

And as Andrei said, a timetable might be the way to go if you have R2016b or later. Of course, if you are just using the table to write to a file via writetable, then you don't need a timetable. You could still convert day,month,year into a datetime so your file has one column in it, that's up to you.