Converting a date in character format to an actual date recognized by MATLAB

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Ryan McBurney 2019-9-17

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https://ww2.mathworks.cn/matlabcentral/answers/480820-converting-a-date-in-character-format-to-an-actual-date-recognized-by-matlab

评论： Ryan McBurney 2019-9-17

I pulled the date from a cell in an excel file that looked like this "Date: 06-Jun-2019 start" without the quotes and shortened it to 06-Jun-2019.

I was originally just putting this date as an annotation on a plot, but now I am running several excel files through the code and I want to collect these dates in a variable called AllDates. When I set this up the code fails because 06-Jun-2019 is sized 1x11 and I'm trying to fill a single index of AllDates.

How can I change the format of 06-Jun-2019 so MATLAB understands its a date. Eventually I need to plot these dates as well.

Here is some code I am using:

for k = 1:numel(Filename)
  File = fullfile(Path, Filename{k});
  [num, txt, raw] = xlsread(File);
  
DateInfo = cell2mat(raw(2,1));
EventDate = DateInfo(1,7:end-6);
EventDate = datetime(EventDate,'InputFormat', 'dd-mm-yyyy');
allDate(k) = EventDate
end

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Ryan McBurney 2019-9-17

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Nice, that helped a lot. Thanks. I changed how I initialized allDate. I accidentally left that out of my code for the sake of less clutter.

allDate = datetime(zeros(1,length(Filename)));
allDate(k) = EventDate;

I also changed the first line of this part of code to how you noted in your answer.

DateInfo = raw{2,1};
EventDate = DateInfo(1,7:end-13);
EventDate = datetime(EventDate,'InputFormat', 'dd-MM-yyyy');

The code doesn't fail, but my allDate output looks like this

allDate = 
[30-Nov--0001 00:00:00,   NaT,      NaT,     NaT,     NaT,   06-Jun-2019 00:00:00 ]

A few more head scratches and I'll get there, unless you have more hints.

Thanks again, Guillaume.

Walter Roberson 2019-9-17

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allDate = datetime(zeros(1,length(Filename)));

would be an error if length(Filename) was not 3 or 6, and for either of those it would create a scalar datetime matrix. If you wanted to create length(Filename) datetimes then you would need that as the number of rows, such as datetime(zeros(length(Filename),3))

But

allDate = NaT(1, length(Filename));

would be better for that situation.

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Answer 1

Guillaume 2019-9-17

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https://ww2.mathworks.cn/matlabcentral/answers/480820-converting-a-date-in-character-format-to-an-actual-date-recognized-by-matlab#answer_392326

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Your

allDate = datetime(zeros(1,length(Filename)));

will only work if length(Filename) is 3 or 6. Otherwise you'll get an error. Even if you don't get an error, your array is initialised with just one datetime: 30 Nov 1 00:00:00

The simplest way to initialise it would be:

allDate = NaT(size(Filename));

which will create a datetime array full of Not A Time.

The code doesn't fail, but my allDate output looks like this

I would expect that if k is 6 and never goes through 1 to 5. allDate consists of that initial datetime(0, 0, 0) you put in there at index 1, NaT (not a time) for flling the indices between 1 and 6, and the value you put in at index 6.