Compact way to extract day and hour from a datetime / datestrings format ?

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Sim 2022-6-27

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评论： Voss 2022-6-28

采纳的回答： Voss

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I have a cell array including datetime / datestrings data, i.e. days and hours.

Here following, I show two examples related to the same day, and 24 hours far from each other:

>> time_array(1)
ans =
  1×1 cell array
    {'17-Jun-2017 0:00:00'}
>> time_array(24)
ans =
  1×1 cell array
    {'17-Jun-2017 23:00:00'}
    
    

Is there any compact way to extract day number (starting from the first day in my dataset) and hour just given the row / index of my dataset, called time_array?

For example, if I give the row / index of my datset, let's say 200:

    >> time_array(200)
ans =
  1×1 cell array
    {'25-Jun-2017 7:00:00'}

is there any compact way to get this output ?

    day = 9
    hour = 7

Indeed, the 25th June is the day number 9 if we start to count from the day number 1, which is the 17th June.

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KSSV 2022-6-27

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t = datetime ;
t.Day
ans = 27
t.Hour
ans = 8

Sim 2022-6-28

编辑：Sim 2022-6-28

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Thanks a lot @KSSV, very kind!

I have realised that my question was not clear and I am really sorry!

Your solution answers my question in the title, and

t.Day

gives me the day that I select from

t

For example:

>> t.Day(200)
ans =
    25

gives me "25" because "t(200)" corresponds to '25-Jun-2017 07:00:00',

>> t(200)
ans = 
datetime
25-Jun-2017 07:00:00

However, in my question description, I asked something slightly different.. Probably, I should rephrase the question...?

What I wanted to know was the day's number corresponding to "t(200)", starting from the first day in my dataset "t(1)"

>> t(1)
ans = 
datetime
17-Jun-2017

In this example, the 25th of June would be the 9th day, if we start counting from the first day of my dataset, i.e. the 17th of June (the 17th of June would be the day number 1, the 18th of June would be the day number 2, and so on...).

In this regard, @Voss provided one possible answer / solution, i.e.

>> floor(days(t(200)-t(1))) + 1
ans =
     9

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Answer 1

Voss 2022-6-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1748695-compact-way-to-extract-day-and-hour-from-a-datetime-datestrings-format#answer_994765

编辑：Voss 2022-6-27

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time_array = { ...
    '17-Jun-2017 0:00:00'; ...
    '17-Jun-2017 1:00:00'; ...
    '17-Jun-2017 2:00:00'; ...
    ...
    '17-Jun-2017 23:00:00'; ...
    '18-Jun-2017 0:00:00'; ...
    ...
    '25-Jun-2017 7:00:00'; ...
    ...
    '31-Jul-2017 13:00:00'; ...
    };
t = datetime(time_array)
t = 7×1 datetime array
   17-Jun-2017 00:00:00
   17-Jun-2017 01:00:00
   17-Jun-2017 02:00:00
   17-Jun-2017 23:00:00
   18-Jun-2017 00:00:00
   25-Jun-2017 07:00:00
   31-Jul-2017 13:00:00
disp(t(end-1));
   25-Jun-2017 07:00:00
floor(days(t(end-1)-t(1))) + 1
ans = 9
t(end-1).Hour
ans = 7
disp(t(end));
   31-Jul-2017 13:00:00
floor(days(t(end)-t(1))) + 1
ans = 45
t(end).Hour
ans = 13

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Answer 2

Sim 2022-6-28

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https://ww2.mathworks.cn/matlabcentral/answers/1748695-compact-way-to-extract-day-and-hour-from-a-datetime-datestrings-format#answer_995505

编辑：Sim 2022-6-28

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Thanks a lot @Voss, your code does what I need... In my case, I did in this way and it works:

t = datetime(time_array); % I found out that "time_array" was not in a "datetime" format
index_dataset = 200; % just an example
number_of_days_from_the_first_one = floor(days(t(index_dataset)-t(1))) + 1;
hour_corresponding_to_index_dataset = t(index_dataset).Hour;