Reading date and time from CSV file in MATLAB

Question

datetime, M01, M02, M03, M04, M05, M06
8/15/2009 0:00, 5.8, 7.8, 7.8, 7.3, 0, 7.9
8/15/2009 0:10, 7.1, 8.1, 8.1, 7.7, 0, 8.1
8/15/2009 0:20, 6.8, 7.4, 7.6, 7.1, 0, 7.3
8/15/2009 0:30, 5.6, 6.8, 7.1, 6.6, 0, 6.8
8/15/2009 0:40, 3.9, 6.2, 6.4, 6.2, 0, 6.4
8/15/2009 0:50, 4.6, 5.5, 6.1, 5.8, 0, 5.6
8/15/2009 1:40, 7, 7, 7.2, 6.9, 0, 6.3

Can you help me to read this CSV file properly so I can convert the first column into a string using datenum? csvread of course does not work. With textscan I am lost how to call it , so I do not get errors. The date and time are in the same column.

Sorry it might sound a dumb question!!!

I know how to read read the above file now. but how do i write it back in a file.txt in the exact same format?? i mean i modified some columns and now need a similar file with same format for column 1 and row 1. Thanks for the help

Answer 1

According to your comment above, if the data looks like:

datetime, M01, M02, M03, M04, M05, M06
8/15/2009 0:00, 5.8, 7.8, 7.8, 7.3, 0, 7.9
8/15/2009 0:10, 7.1, 8.1, 8.1, 7.7, 0, 8.1
8/15/2009 0:20, 6.8, 7.4, 7.6, 7.1, 0, 7.3
8/15/2009 0:30, 5.6, 6.8, 7.1, 6.6, 0, 6.8
8/15/2009 0:40, 3.9, 6.2, 6.4, 6.2, 0, 6.4
8/15/2009 0:50, 4.6, 5.5, 6.1, 5.8, 0, 5.6
8/15/2009 1:40, 7, 7 7.2, 6.9, 0, 6.3

then use the following to read it as a matrix:

fid = fopen('file.csv', 'rt');
a = textscan(fid, '%s %f %f %f %f %f %f', ...
      'Delimiter',',', 'CollectOutput',1, 'HeaderLines',1);
fclose(fid);

format short g
M = [datenum(a{1}) a{2}]

... and the output I get:

M =
    7.34e+005        5.8        7.8        7.8        7.3          0        7.9
    7.34e+005        7.1        8.1        8.1        7.7          0        8.1
    7.34e+005        6.8        7.4        7.6        7.1          0        7.3
    7.34e+005        5.6        6.8        7.1        6.6          0        6.8
    7.34e+005        3.9        6.2        6.4        6.2          0        6.4
    7.34e+005        4.6        5.5        6.1        5.8          0        5.6
    7.34e+005          7          7        7.2        6.9          0        6.3

if you set the display format to a long output, you will see the full numbers (note they are still stored in full), or use fprintf:

fprintf('%.9f\n', M(:,1))

734000.000000000
734000.006944445
734000.013888889
734000.020833333
734000.027777778
734000.034722222
734000.069444445

Answer 2

TEXTSCAN by itself won't convert the date, but you can call DATENUM on just the column that needs it.

f = fopen('datafile.txt');
data = textscan(f, '%s %f %f %f %f %f %f', 'Delimiter', ',', 'HeaderLines', 1);
fclose(f);
data{1} = datenum(data{1});

will return a cell array data of doubles where the first column is the MATLAB datenum corresponding to each date, and each other column is the corresponding column from the file.