MATLAB: How to create a vector with the first day of each month

vector;months;first;date

How do I create a column vector with the first day of each month? Considering I have a list of days…

Best Answer

Not quite sure what you are asking for here.
I assume you have a vector with all days from Monday-Sunday, and you know which day the first day of the year is:
weekdays = [{'Monday'},{'Tuesday'},{'Wednesday'},{'Thursday'},{'Friday'},{'Saturday'},{'Sunday'}];
dayNumber = zeros(1,12);
dayNumber(1) = 2;       % 2013 started on a Tuesday.
numDays = [31 28 31 30 31 30 31 31 30 31 30 31];  % Not a leap year
for i = 1:11
  dayNumber(i+1) = mod((dayNumber(i)+days(i)-1),7)+1; 
end
for i = 1:12
  dayName(i) = weekdays(dayNumber(i));
end
If you need to account for leap years: It is a leap year every fourth year, except years that can be divided by 100, except years that can be divided by 400.
A general approach would be something like this:
year = 2013;
year0 = 1900;
startDay = 1;  % Year 1900 started on a monday.
if year > year0
  for i = 1:(year-year0)
    if mod((year0+i),4)~=0
      startDay = startDay + 365;
    elseif mod((year0+i),4)==0 && mod((year0+i),100)~=0
      startDay = startDay + 366;
    elseif mod((year0+i),4)==0 && mod((year0+i),100)==0 && mod((year0+i),400)~=0
      startDay = startDay + 365;
    elseif mod((year0+i),4)==1 && mod((year0+i),400)==0
      startDay = startDay + 366;
    end
  end
end
dayNumber = mod(startDay,7)+1;
This gives dayNumber = 2, for year = 2013. Then continue with the code above. (numDays(2)=29, if leap year)
Related Question