How to make a loop to find average of each month

1 次查看（过去 30 天）
Kristine
Kristine 2014-6-20
评论： Kristine 2014-6-23
I have a data set of monthly averages and would like to make a loop to get an average of every month, so the average of every January, February, and etc.
Here is my data:
1973 1 144.46 4.68
1973 2 118.77 5.05
1973 3 57.76 7.42
1973 4 103.44 6.01
1973 5 84.11 6.18
1973 6 74.74 6.11
1973 7 64.86 6.46
1973 8 69.95 6.07
1973 9 75.25 5.66
1973 10 91.90 5.64
I can do it the hard way:
a=find(vinddata_mean_monthly(:,2)==1);
jan=vinddata_mean_monthly(a,:);
jan_dir=mean(jan(:,3));
jan_spd=mean(jan(:,4));
..
But if anyone could help my make a loop, help would be greatly appreciated.
Kristine

请先登录，再回答此问题。

采纳的回答

dpb
dpb 2014-6-21
编辑：dpb 2014-6-21
mndata=zeros(12,2); % preallocate
for m=1:12 % over each month
mndata(m,:)=mean(vinddata_mean_monthly(vinddata_mean_monthly(:,2)==m,3:4));
end
ADDENDUM
If the data file is regular in not having any missing months, then one can set the row indices directly and eliminate the logical addressing. Unless the size of the data file is humongous it'll likely not be of any real difference, but still...
for m=1:12
mx(m,:)=mean(vinddata_mean_monthly(m:12:end,3:4)); % take every 12th row
end

更多回答（1 个）

Cedric
Cedric 2014-6-21
编辑：Cedric 2014-6-21
Here is one solution if you need monthly means over all years [mean(Jan73,Jan74,..); mean(Feb73,Feb74,..); ..]:
dir_monthly = accumarray( data(:,2), data(:,3), [12,1], @mean ) ;
spd_monthly = accumarray( data(:,2), data(:,4), [12,1], @mean ) ;
where data is what you named vinddata_mean_monthly in your question. This works if there are missing data.
  2 个评论
dpb
dpb 2014-6-21
Yeah, it's that the input to accumarray must be a vector so couldn't figure out anything that wasn't either a double as you wrote or over accumarray itself that I went w/ the loop, Cedric.
Cedric
Cedric 2014-6-21
编辑：Cedric 2014-6-21
I often test/profile the loop as well to be honest. Sometimes we think that we do better than a loop with ACCUMARRAY and we end up using CELLFUN/ARRAYFUN/etc to prepare indices because there is no way to get them drectly. And we are mistaken because it looks more elegant and concise but it is not as efficient overall.
Yet, when we are lucky enough to be in a situation where ACCUMARRAY can be used directly, it is difficult to beat.

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by