How to write a LOOP for this case?

Question

BN 2019-10-28

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https://ww2.mathworks.cn/matlabcentral/answers/487729-how-to-write-a-loop-for-this-case

评论： BN 2019-10-28

采纳的回答： Guillaume

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Hey all

I have 34 variable in my workplace like this:

precip_1982_daily

precip_1983_daily

precip_1984_daily

precip_1985_daily

...

precip_2015_daily

I want to use this if code below:

if size(precip_1982_daily,3)==365
    month_lengths=[31 28 31 30 31 30 31 31 30 31 30 31];%non-leap year
else
    month_lengths=[31 29 31 30 31 30 31 31 30 31 30 31];%leap year
end
precip_1982_monthly=mat2cell(precip_1982_daily,size(precip_1982_daily,1),size(precip_1982_daily,2),month_lengths);%divide into 1 cell per month
precip_1982_monthly=cellfun(@(x) nansum(x,3),precip_1982_monthly,'UniformOutput',false);%find mean for each month
precip_1982_monthly=cell2mat(precip_1982_monthly);%convert back to 3D array

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Answer 1

Guillaume 2019-10-28

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So again, numbered variables and field names are a bad idea. (see here and here) for the related questions). The whole thing would be simpler if the original cell array was used.

If the original cell array had been kept, the code over the 3 questions could be simplified to:

%using original cell array precips
precip_monthly = cell(size(precips));  %preallocate result cell array
for idx = 1:numel(precips)
    if size(precips{idx}, 3) == 365
        month_lengths=[31 28 31 30 31 30 31 31 30 31 30 31];%non-leap year
    else
        month_lengths=[31 29 31 30 31 30 31 31 30 31 30 31];%leap year
    end
    p_month =mat2cell(precips{idx}, size(precips{idx}, 1), size(precips{idx}, 2), month_lengths);%divide into 1 cell per month
    p_month = cellfun(@(x) sum(x, 3, 'omitnan'), p_month, 'UniformOutput', false); %find mean for each month !!THIS CALCULATE THE SUM!!
    precip_monthly{idx} = cell2mat(p_month);%convert back to 3D array
end

Note that you have written a comment that says find mean for each month but you use the sum function. So either the code or the comment is wrong.

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BN 2019-10-28

I greatly appreciate your responses.

special thanks to both of you :)

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Answer 2

Shubham Gupta 2019-10-28

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https://ww2.mathworks.cn/matlabcentral/answers/487729-how-to-write-a-loop-for-this-case#answer_398449

编辑：Shubham Gupta 2019-10-28

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I think this is the continuation of this question.

So, once you create struture as mentioned in the above answer, you can use:

for i = 1:length(precip)
    precip_daily = precip.(['y',num2str(i+1981)]); % Access data of specific year
    if size(precip_daily,3)==365
        month_lengths=[31 28 31 30 31 30 31 31 30 31 30 31];%non-leap year
    else
        month_lengths=[31 29 31 30 31 30 31 31 30 31 30 31];%leap year
    end
    precip_monthly=mat2cell(precip_daily,size(precip_daily,1),size(precip_daily,2),month_lengths);%divide into 1 cell per month
    precip_monthly=cellfun(@(x) nansum(x,3),precip_monthly,'UniformOutput',false);%find mean for each month
    precip_monthly=cell2mat(precip_monthly);%convert back to 3D array
    precp_monthly.(['y',num2str(i+1981)]) = precip_monthly;  % Create precip_monthly structure 
end