MATLAB: Converting date times into periods, day, month

conversiondatetimeMATLAB

Hi,

I have a list of datetimes, and I want to convert it to Month No., Day No. Period No. Where Period No. is the number of the half hour in the day, where 00:00 is Period 1. and 23:30 is Period 48. An example of the datetimes is as follows:

Ideally I will want to have 3 resultant columns. This is used for determining how things would be expected to run at a given period/day/month. There are other structures besides this, but this will help me on my way. Is there any simple way of doing this? I did use a couple of loops from an old way, but I am getting the data from a database now, rather than a flat file so I want to make it more efficient.

Thanks,

James

Best Answer

I would try something like this:

T = table();
[~,T.Month,T.Day] = ymd(FC.StartDateTime);
[h,m] = hms(FC.StartDateTime);
[~,T.period] = ismember((h +(m/60)),(0:.5:24));

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MATLAB: Time series data with missing dates to remap to calendar days vector

If you have R2014b or later, use tables and datetimes. For the specific question you've asked, simplest to use ismember and indexing:

>> Date = datetime({'01/01/2015';'01/14/2015';'05/30/2015'});
>> Value = [10; 5; 10];
>> TSomeDays = table(Date,Value)
TSomeDays =
       Date        Value
    ___________    _____
    01-Jan-2015    10   
    14-Jan-2015     5   
    30-May-2015    10   
>> Date = datetime(2015,1,(1:180)');
>> Value = zeros(size(Date));
>> TAllDays = table(Date,Value);
>> [~,i] = ismember(TSomeDays.Date,TAllDays.Date)
i =
     1
    14
   150
>> TAllDays.Value(i) = TSomeDays.Value
TAllDays =
       Date        Value
    ___________    _____
    01-Jan-2015    10   
    02-Jan-2015     0   
[snip]
    13-Jan-2015     0   
    14-Jan-2015     5   
    15-Jan-2015     0   
[snip]
    29-May-2015     0   
    30-May-2015    10   
    31-May-2015     0   
[snip]
>> Date = datetime(2015,1,(1:365)');
>> TAllDays = table(Date);

Another possibility is to use an outer join, which may be too heavy of a hammer for this specific question, but which provides capabilities that you may yet need. outerjoin fills missing values with NaN, but you can put zeros in their place:

>> TAllDays = outerjoin(TAllDays,TSomeDays,'Key','Date','MergeKeys',true)
TAllDays =
  365×2 table
       Date        Value
    ___________    _____
    01-Jan-2015     10  
    02-Jan-2015    NaN  
    03-Jan-2015    NaN  
[snip]
    13-Jan-2015    NaN  
    14-Jan-2015      5  
    15-Jan-2015    NaN  
[snip]
    29-May-2015    NaN  
    30-May-2015     10  
    31-May-2015    NaN  
[snip]
>> TAllDays.Value(isnan(TAllDays.Value)) = 0
TAllDays =
       Date        Value
    ___________    _____
    01-Jan-2015    10   
    02-Jan-2015     0   
[snip]
    13-Jan-2015     0   
    14-Jan-2015     5   
    15-Jan-2015     0   
[snip]
    29-May-2015     0   
    30-May-2015    10   
    31-May-2015     0   
[snip]

If you have R2016b, this is trivial using a timetable:

>> Date = datetime(2015,1,(1:365)');
>> TTAllDays = retime(TTSomeDays,Date,'FillWithConstant','Constant',0)
TTAllDays =
        Date       Value
    ___________    _____
    01-Jan-2015    10   
    02-Jan-2015     0   
[snip]
    13-Jan-2015     0   
    14-Jan-2015     5   
    15-Jan-2015     0   
[snip]
    29-May-2015     0   
    30-May-2015    10   
    31-May-2015     0   
[snip]

MATLAB: Define time period for each year

[y, m, d] = ymd(YourDataTable.Date);
mask = m >= sm & m <= em & (m > sm | d >= fd) & (m < em | d <= ld);
selected_entries = YourDataTable(mask,:);

Best Answer

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MATLAB: Time series data with missing dates to remap to calendar days vector

MATLAB: Define time period for each year

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