Creating List of Dates, Stepping by a Month
Ever need to create a vector of dates using some sort of pattern? Perhaps these will be used as the edges argument for a histogram, with each a month.
What's the best way to create a datetime array where each element is the first of the month? And what does "best" even mean? - fewest keystrokes, fewest function calls, most readable, most flexible, most maintainable,etc. Suppose I want to produce something like this:
2018-Jan-01, 2018-Feb-01, 2018-Mar-01, ...
In fact, there are lots of suitable ways. Here are a few.
Simply Use datetime
Just use datetime and specify the month vectors. This works
mydates1 = datetime(2018,1:12,1)
mydates1 = 1×12 datetime array Columns 1 through 5 01-Jan-2018 01-Feb-2018 01-Mar-2018 01-Apr-2018 01-May-2018 Columns 6 through 10 01-Jun-2018 01-Jul-2018 01-Aug-2018 01-Sep-2018 01-Oct-2018 Columns 11 through 12 01-Nov-2018 01-Dec-2018
While I'm at it, I can find the number of days in each month I have, using eomday.
numDays = eomday(year(mydates1),month(mydates1)); bar(mydates1,numDays)
What if Months Span Years?
If the months in question span years, you can do this fairly compactly using calmonths.
mydates2 = datetime(2017,1,1):calmonths(1):datetime(2018,7,1)
mydates2 = 1×19 datetime array Columns 1 through 5 01-Jan-2017 01-Feb-2017 01-Mar-2017 01-Apr-2017 01-May-2017 Columns 6 through 10 01-Jun-2017 01-Jul-2017 01-Aug-2017 01-Sep-2017 01-Oct-2017 Columns 11 through 15 01-Nov-2017 01-Dec-2017 01-Jan-2018 01-Feb-2018 01-Mar-2018 Columns 16 through 19 01-Apr-2018 01-May-2018 01-Jun-2018 01-Jul-2018
In addition, you can go beyond 12 months and datetime still works as expected, without needing calmonths.
mydates3 = datetime(2018,1:24,1);
mydates4 = datetime(2017,7:18,1)
mydates4 = 1×12 datetime array Columns 1 through 5 01-Jul-2017 01-Aug-2017 01-Sep-2017 01-Oct-2017 01-Nov-2017 Columns 6 through 10 01-Dec-2017 01-Jan-2018 01-Feb-2018 01-Mar-2018 01-Apr-2018 Columns 11 through 12 01-May-2018 01-Jun-2018
However keeping track of the relative month shifts to start has its own mental overhead for me.
Another Way Using calmonths
Try this instead. Find the right start date, and then add on the correct number of calmonths from there.
mydates5 = datetime(2017,7,1) + calmonths(0:11)
mydates5 = 1×12 datetime array Columns 1 through 5 01-Jul-2017 01-Aug-2017 01-Sep-2017 01-Oct-2017 01-Nov-2017 Columns 6 through 10 01-Dec-2017 01-Jan-2018 01-Feb-2018 01-Mar-2018 01-Apr-2018 Columns 11 through 12 01-May-2018 01-Jun-2018
Do you have another way you like to produce lists of dates? What's your preference for these sorts of situations? Let me know here.
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