Create a monthly date vector of serial numbers

Hi everyone,

I spent hours trying this and I am sure it must be easy but I can't get my head around it. What I want is to create a vector that contains serial numbers for each month for 30 years, so that I can use this vector for the x axis of a plot. (so e.g. I want Jan 1990, Feb 1990, March 1990 etc in serial numbers)

why doesn't something simple like this work? datenum({'01-Jan-1900':'01-Nov-2011'})

Any help is appreciated Thanks so much Sandra

Answer 1

[Oleg Komarov]

You are "almost" right, but what you're saying to matlab with,

datenum({'01-Jan-1900':'01-Nov-2011'})

is:

"Take the string '01-Jan-1900' (which has numeric value of 48 49 45 74 97 110 45 49 57 48 48) and apply the colon operator till the string '01-Nov-2011' (48 49 45 78 111 118 45 50 48 49 49)"

what you have to do is first convert the string to serial dates and then apply the colon...but this approach is not precise because you want one month intervals and months are irregular.

The solution is the following:

datenum(1900,1:120,1)

The months in excess of the first year will augment the year to 1901 and so on.

[Fangjun Jiang]

Excellent! Sounds like a useful trick!

[Sandra]

Thanks so much, I knew there must be a trick:-)

Answer 2

[Walter Roberson]

[Y,M] = meshgrid(1900:1929, 1:12);
TheSerialDates = datenum([Y(:), M(:), ones(numel(Y),1)]);

[Fangjun Jiang]

The order is not right. diff(TheSerialDates ) will show it.

[Walter Roberson]

Thanks for catching that. I have fixed it now. I think that's the first time I ever found a use for meshgrid() !

[Suene]

This solution also worked for me. Many thanks!

Answer 3

[Fangjun Jiang]

x=bsxfun(@(Month,Year) datenum(Year,Month,1),(1:12).',1980:2010);
x=x(:);
diff(x)

[Suene]

thanks for sharing! It worked for me! :)

Answer 4

[Steven Lord]

With datetime and calendarDuration there are a couple different ways to create this vector.

The first technique just adds calendar months to the starting date.

startDate = datetime('January 1, 1990');
V1 = startDate + calmonths(0:30*12-1); % 30 years = 30*12 calendar months

The second technique adds between 0 and 11 calendar months and between 0 and 29 calendar years to the starting date. This uses implicit expansion to add the months and years together to form a matrix. I reshape that matrix when I compute V2 to make it the same size and orientation as V1. If you wanted something more like a planner view, look at V2planner.

startDate = datetime('January 1, 1990');
oneYearInMonths = calmonths(0:11);
thirtyYearsInYears = calyears(0:29);
monthsPlusYears = oneYearInMonths.' + thirtyYearsInYears;
V2 = startDate + reshape(monthsPlusYears, 1, []);
V2planner = startDate + monthsPlusYears;

This next one takes advantage of the fact that the datetime function is not limited to accepting only month numbers between 1 and 12. The 13th month of 1990 is actually January 1991.

monthlist = 1:30*12;
V3 = datetime(1990, monthlist, 1);

Do these give the same result?

isequal(V1, V2)
isequal(V2, V3)
isequal(V1, V3)

Answer 5

[Navid Ghajarnia]

This is another answer to this question:

t1 = datetime(1900,01,01);
t2 = datetime(2011,11,01);
t(:,1) = t1:t2;
Dates_Daily = [year(t), month(t)];
Dates_Monthly = unique(Dates_Daily,'rows');