# <randum number generation

4 views (last 30 days)
Johannes Deelstra on 18 Mar 2014
Commented: Johannes Deelstra on 28 Mar 2014
Hei, I have a time series for day and observation for a period of 365 days in variable a, a(:,1) being the daynumber (1 - 365) and a(:,2) the observations. I need to randomly select a day every week, so the first selection has to be a number from 1 - 7, the second day has to be a number between 8 - 14, etc. The selected daynumber have to be entered in a new variable (b). How is this done? Thanks for helping, Johannes.

Carlos on 18 Mar 2014
Edited: Carlos on 18 Mar 2014
In r you have the numbers you requested
r=zeros(52,1);
pointer=0;
for k=1:52
r(k)=pointer+(1+round(7*rand));
pointer=pointer+7;
end

Niklas Nylén on 18 Mar 2014
If we assume that the first day in the array also is the start of a week it is necessary to generate 52 random days during a 365 day period. Since 52*7 = 364 it the final day must be day 365 since it is the only day in that week.
Start of by generating 52 random integers in the range [1,7].
randomWeekdays = randi(7,1,52);
Next, translate the numbers to days in the year
b = randomWeekdays+(0:7:358);
Johannes Deelstra on 28 Mar 2014
A bit late but thanks very much to both, answering my question concerning random number generation. Regards Johannes