using datetime() in retrieving data

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MA 2021-9-30

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https://ww2.mathworks.cn/matlabcentral/answers/1463754-using-datetime-in-retrieving-data

评论： MA 2021-10-2

采纳的回答： Siddharth Bhutiya

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Assuming I am using datetime() to refer to the date and time that some data has accured in.

date=datetime(1999,06,19,15,45,00); %datetime(year,month,day,hour,min,sec)

I am using 'date' in further comparison to retrive some data, now is there any syntax I may use in this that would allow me for example to retrive the data happened in a certain day for all the years, (ex: the data happened in 1st october from all the years we have) or for a certain hour from all days in months in years?

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Steven Lord 2021-9-30

How is your data stored? If it's in a timetable array you may find a timerange useful. The isbetween function may also be helpful.

Alternately checking using some of the functions in the "Split Dates and Times" section on the Dates and Times page in the documentation may be of use as @Siddharth Bhutiya showed.

MA 2021-10-2

Thank you, the documentation you suggested helped a lot!. I was using different way for comparison but isbetween made it really simple, thanks a lot.

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Answer 1

Siddharth Bhutiya 2021-9-30

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Once you have created a datetime array, you could use functions like month, day, year, etc to get the corresponding field values from the datetime. Then as KSSV suggested above, you could use those to index and filter your datetimes.

>> d
d = 
  4×1 datetime array
   01-Oct-2020
   02-Oct-2021
   01-Oct-2019
   01-Sep-2018
>> month(d)
ans =
    10
    10
    10
     9
>> d(month(d) == 10 & day(d) == 1) % Get 1st October for all years
ans = 
  2×1 datetime array
   01-Oct-2020
   01-Oct-2019

If you want to filter your datetimes for values between two points in time then you could also use something like isbetween: https://www.mathworks.com/help/matlab/ref/datetime.isbetween.html

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MA 2021-10-2

thank you that was really helpful, using these functions sorted the issue for me, that was excatly what I needed.

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Answer 2

KSSV 2021-9-30

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Read about datevec. This will split your date into year, month, day, hour, minute and secobd. From here you can use logial indexing and get the indices.

idx = month == 10 & day == 1 ;