MATLAB: Creating index from datetime vector days

ymd indexing

Hi,

I have a 100×1 datetime vector. I have extracted the values of the day using the ymd function: [~,~,d] = ymd(input).

How can I create a vector with a unique identifier for every period from the 15th to the 14th in the days vector, d (each sequence of 15 to the next 14). (i.e. from jan 15 – feb 14, i could have 1's, from feb 15 – mar 14, i can have 2s, etc.)

Any help would be appreciated. Thx in advance!

Best Answer

Take the month number output as well as the day output. If the day is less than 15, subtract 1 from the month number to get the index (if the month number was 1, substitute 12 for previous year); otherwise use the month number directly.

Related Solutions

MATLAB: Select row from matrix based on month with datenum

Please attach file with your datas (A and B):

out = B(A(month(datetime(B(:,1),'InputFormat','yyyy-MM-dd'))) > B(:,9),:);

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]

Best Answer

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

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