csv reading related matter

Question

jie hu 2023-12-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2064561-csv-reading-related-matter

评论： Star Strider 2023-12-28

采纳的回答： Star Strider

2009.csv

在 MATLAB Online 中打开

I have created a .csv file with date and value by

  fid=fopen([file(1:4) '.csv'],'w');
    fprintf(fid,'%s,%s,%s\n', 'Time','u10','v10');
    for i =1:length(t_seris)
        fprintf(fid,'%s,%8.4f,%8.4f\n',t_seris(i),u10_p_vct(i),v10_p_vct(i));
    end
    fclose(fid);

the .csv file generated is '2009.csv'. However, in this file, I found that from line #290, the time format is changed. Then when I import this .csv by table= readtable('2009.csv'), the time column information is gone. May I know what is wrong?

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jie hu 2023-12-28

编辑：KSSV 2023-12-28

在 MATLAB Online 中打开

2009.zip

% original file is in the .zip file, which is a .nc file after unzip. below the code is what i used to extract data from .nc and create the .csv
VelFiles=dir('./20*.nc');
Nf=length(VelFiles);
for n=1:1
    
    file=VelFiles(n).name(1:end);
    
    % load .nc time
    timeout=double(ncread(file,'time'));
    t_seris=datetime('1900-01-01 00:00') + hours(timeout);
    datetime.setDefaultFormats('reset','dd/MM/yyyy HH:mm');
    
    % load .nc wind data
    u10=double(ncread(file,'u10')); v10=double(ncread(file,'v10'));
    % take the nearest grid (lower_lon & lower_lat) to the point
    u10_p = u10(1,2,:); v10_p = v10(1,2,:);
    % convert matrix to column vector
    u10_p_vct=u10_p(:); v10_p_vct=v10_p(:);
    
    fid=fopen([file(1:4) '.csv'],'w');
    fprintf(fid,'%s,%s,%s\n', 'Time','u10','v10');
    for i =1:length(t_seris)
        fprintf(fid,'%s,%8.4f,%8.4f\n',datestr(t_seris(i)),u10_p_vct(i),v10_p_vct(i));
    end
    fclose(fid);
    
end

KSSV 2023-12-28

Why to write to csv when already you have data in good and nice nc file? You may consider using readtable to read csv file.

jie hu 2023-12-28

Hi KSSV, it is for further other operations on csv

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Answer 1

Star Strider 2023-12-28

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2064561-csv-reading-related-matter#answer_1378996

在 MATLAB Online 中打开

2009.zip

Thje problem is your not taking full advantage of MATLAB table arrays and everything they can do.

Try this —

Uz = unzip('2009.zip');
file = Uz{1}
file = '2009.nc'
% Info = ncinfo(Uz{1});
% Vbls = Info.Variables;
% Vbls.Datatype;
% Vbls.Name;
% Vbls(3).Attributes.Value;
Time = datetime(1900,1,1) + hours(ncread(file,'time'));
Time.Format = 'dd/MM/yyyy HH:mm';
    % datetime.setDefaultFormats('reset','dd/MM/yyyy HH:mm');
    % load .nc wind data
    u10=double(ncread(file,'u10')); v10=double(ncread(file,'v10'));
    % take the nearest grid (lower_lon & lower_lat) to the point
    u10_p = u10(1,2,:); v10_p = v10(1,2,:);
    % convert matrix to column vector
    u10_p_vct=u10_p(:); v10_p_vct=v10_p(:);
u10 = u10_p_vct;
v10 = v10_p_vct;
T2009 = table(Time,u10,v10)                         % Create Table
T2009 = 8760×3 table
          Time            u10        v10  
    ________________    _______    _______

    01/01/2009 00:00    -2.4284     -3.566
    01/01/2009 01:00    -3.0311    -4.4606
    01/01/2009 02:00    -3.8908    -4.6728
    01/01/2009 03:00    -4.0842    -4.1387
    01/01/2009 04:00    -4.0012    -4.0258
    01/01/2009 05:00     -3.707     -3.966
    01/01/2009 06:00     -3.985    -4.0958
    01/01/2009 07:00    -4.2243    -3.9444
    01/01/2009 08:00    -4.3457    -3.6828
    01/01/2009 09:00    -4.5298    -3.3928
    01/01/2009 10:00    -4.8411    -2.5877
    01/01/2009 11:00    -4.6303    -3.6123
    01/01/2009 12:00    -4.0321    -4.0495
    01/01/2009 13:00    -2.7064    -3.5143
    01/01/2009 14:00    -2.1252    -3.1412
    01/01/2009 15:00    -1.8353    -3.1889
writetable(T2009, '2009.csv')                       % Write Table To File
T2009_2 = readtable('2009.csv');                    % Check Result
T2009_2.Time.Format = 'dd/MM/yyyy HH:mm'            % Regenerate Desired Time Format
T2009_2 = 8760×3 table
          Time            u10        v10  
    ________________    _______    _______

    01/01/2009 00:00    -2.4284     -3.566
    01/01/2009 01:00    -3.0311    -4.4606
    01/01/2009 02:00    -3.8908    -4.6728
    01/01/2009 03:00    -4.0842    -4.1387
    01/01/2009 04:00    -4.0012    -4.0258
    01/01/2009 05:00     -3.707     -3.966
    01/01/2009 06:00     -3.985    -4.0958
    01/01/2009 07:00    -4.2243    -3.9444
    01/01/2009 08:00    -4.3457    -3.6828
    01/01/2009 09:00    -4.5298    -3.3928
    01/01/2009 10:00    -4.8411    -2.5877
    01/01/2009 11:00    -4.6303    -3.6123
    01/01/2009 12:00    -4.0321    -4.0495
    01/01/2009 13:00    -2.7064    -3.5143
    01/01/2009 14:00    -2.1252    -3.1412
    01/01/2009 15:00    -1.8353    -3.1889

I changed your code slightly to make it a bit easier for me to work with. Change it back if you like, however please keep the table arrays! They make this straightforward.

.