how to calculating monthly average?

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Lilya
Lilya 2016-5-8
评论： Lilya 2016-5-13
hi all I just want to be sure about this small monthly averaging code
I=1;
for i=1: length(x)/30;
y(i)=mean(x(I:I+29));
L(i)=min(x(I:I+29));
U(i)=max(x(I:I+29));
I=I+29;
end
where x is data matrix (365 day)
thank you
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Star Strider
Star Strider 2016-5-8
Well, some of the data, but not what we need to do what you want with it.
Without knowing the times (at least months-days-years, in some format) at which these are collected, it’s not possible to separate them by month.

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Image Analyst
Image Analyst 2016-5-8
Try this:
dailyValues = rand(1,365); % Sample data
daysInMonths = [31,28,31,30,31,30,31,31,30,31,30,31]
monthEnds = [0, cumsum(daysInMonths)]
for m = 1 : length(monthEnds)-1
firstDay = monthEnds(m)+1;
lastDay = monthEnds(m+1);
fprintf('For month #%d, the first day = %d and the last day = %d\n',...
m, firstDay, lastDay);
monthlyAverage(m) = mean(dailyValues(firstDay:lastDay));
end
% Echo to command window.
monthlyAverage
Of course you need to take leap years into account, which I didn't do.
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Image Analyst
Image Analyst 2016-5-13
JanuaryDailyAmounts = dailyValues(1:31);
FebruaryDailyAmounts = dailyValues(32:59);
MarchDailyAmounts = dailyValues(60:90);
and so on for months ending at rows 120 151 181 212 243 273 304 334 365.
You will then have 12 matrices.
Lilya
Lilya 2016-5-13
I appreciate your help. Thank you.

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Steven Lord
Steven Lord 2016-5-12
Find the month number (either directly from the file or using some of the tools associated with datetime objects then use the month numbers as the subscripts in a call to accumarray, specifying @mean as the accumulation function.
numRows = 30;
X = [randi(12, numRows, 1), randi(100, numRows, 1)] % Column 1 is month, column 2 is data
Y = accumarray(X(:, 1), X(:, 2), [], @mean)

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