Read and write csv files without changing properties

Question

Jake 2020-3-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510021-read-and-write-csv-files-without-changing-properties

评论： Jake 2020-3-11

采纳的回答： Ameer Hamza

Sample_02.csv

I've succesfully solved a big problem thanks to you guys and now I'm facing a slightly smaller but important one.

(Following code is the original one posted by another mvp here. Kudos)

data = int64(csvread('Sample_02.csv')); 
time = data(:,2);
% remove empty rows
data = data(time>0, :);
time = time(time>0);
time = mod(time, 1000000); % yyyymmdd are not important so discard them
current_time = 00000;   % time in hhmmss format
while size(data, 1) > 0
    next_time = current_time + 30000; % 30000 represent 3 hours
    index = time < (current_time + 30000);
    partial_data = data(index, :);
       
     dlmwrite(['data-' num2str(current_time/10000) '-' num2str(next_time/10000) '.csv'], ...
         partial_data, 'precision', '%i');
    
    data(index,:) = [];
    time(index,:) = [];
    current_time = current_time + 30000;
end

The code reads the sample CSV file and split it in to seperate csv files based on time-stamps.

My problem is: The original csv file (Sample_02.csv) has 7 columns and the above code only deals with the second one. Output files also have 7 columns, obviously, but the values are not shown/stored as decimals. For example, the original CSV file stores 123.456789 in its 6th column but the generated output files have only 123 in the respective 6th column.

How can I store the same data as decimals in the output files?

TIA!

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Mohammad Sami 2020-3-10

I tested your sample file with readtable and writetable. It seems to work as you desire. I am using R2019b.

Jake 2020-3-11

You mean the output data were in the format with decimals? I'm using R2017a and it didn't work for some reason :(

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Answer 1

Ameer Hamza 2020-3-11

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https://ww2.mathworks.cn/matlabcentral/answers/510021-read-and-write-csv-files-without-changing-properties#answer_419574

编辑：Ameer Hamza 2020-3-11

Hi James, I posted the answer to your other question. You can just replace the line

data = int64(csvread('Sample_02.csv'));

to

data = csvread('Sample_02.csv');

and it will retain the decimal part of the numbers.

I initially used int64 to preserve precision in the 2nd column, but since it has 14 digits, so it can be handled without int64 too.

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Jake 2020-3-11

Yes! I did this and it works.

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Answer 2

Walter Roberson 2020-3-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510021-read-and-write-csv-files-without-changing-properties#answer_419381

fileread to read the file into a string.

textscan the string to extract the datetime as numeric.

Now regexp the string with '\r?\n', 'split' to create a cell array in which each entry is a line.

Use the information in the numeric date to figure out where to split. The indices can be used in the cell array of split lines. strjoin() those cells with '\n' and fwrite() the result.

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Walter Roberson 2020-3-11

S = fileread(filename);
fmt = '%*f,%ld,%*s';
C2 = cell2mat(textscan(S, fmt));
lines = regexp(S, '\r?\n', 'split');
time = double(mod(C2, 1e6));
 ...
  mask = start_time <= time & time < end_time;
  subset = strjoin(lines(mask), '\n') ;
  fwrite(fid, subset);