Find average for each year

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akk 2018-12-9

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https://ww2.mathworks.cn/matlabcentral/answers/434782-find-average-for-each-year

评论： dpb 2018-12-18

Hi,

I have a column of years (yr) and a column of temperatures (temp). Both columns are 100000 data points long. I would like to circulate through all the data to find an average temp for each year (1996-2018). Im still learning how to write for loops. This is what I have so far:

k=1996;
for j=[1996:2018]; %years range from 1996-2018
        k=k+1;
        idx=find(yr==j);
        meanT=mean(temp(idx));
end

Thanks for your help!

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Answer 1

dpb 2018-12-9

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That should work fine excepting you didn't allocate for the different means by year and overwrote the variable meanT on each iteration so all you have in the end is the last year average.

You could do something like:

yr1=min(yr); yr2=max(yr);              % find first, last year in vector
meanT=zeros(yr2-yr1+1,1);              % allocate vector for each year mean
k=0;                                   % initialize mean storage counter
for j=yr1:yr2                          % iterate over the year range found
  k=k+1;                               % increment counter
  meanT(k)=mean(temp(yr==j));          % compute mean for the year
end

NB: don't need find, the logical addressing vector works to return those locations w/o computing the indices explicitly.

This is fine for learning; the "Matlab way" is to use vector operations instead of loops -- investigate putting your data into a timetable and use the retime function to do this almost automagically.