Create arrays of observations

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CARLOTTA DENTICO
CARLOTTA DENTICO 2021-8-4
评论： Rik 2021-8-4
Hello everybody,
Probably it is a very silly question but I am struggling on it..
I have a series of observations saved as 'pt_mean_lev1_1' up to 'pt_mean_lev1_348' (see picture below) and I want to make an array of them being a = 1x348. How can I do that?
Thank you very much!
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CARLOTTA DENTICO
CARLOTTA DENTICO 2021-8-4
These are monthly mean of temperature spatially averaged over a specific area of the world, for every months for 29 years (I have a total of 348 means i.e 12x29) that I have extracted from a NetCDf file..
I need these means since I need to calculate time series of winter months and summers months and calculate the mean of winter months in the 29 years and mean of summer months.
All that is to calculate the anomalies
CARLOTTA DENTICO
CARLOTTA DENTICO 2021-8-4
lon = ncread('topaz_V4_myocean_arctic_grid1to8_da_class1_19910115.nc', 'longitude');
lat = ncread('topaz_V4_myocean_arctic_grid1to8_da_class1_19910115.nc', 'latitude');
fram = (lon>=0 & lon<=20 & lat>=76 & lat<=80);
for k = 1:348
eval(['pt_lev1_' ,num2str(k), ' = reshape(pt_lev1(:,:,',num2str(k),'),[],1);']);
eval(['pt_mean_lev1_', num2str(k), '= mean(pt_lev1_',num2str(k),'(fram,:),1,''omitnan'');']);
end

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采纳的回答

Sulaymon Eshkabilov
Here is one of the viable solutions with dynamically naming variables and attaining their values from the workspace.
a = [];
for ii=1:348
Var = strcat('pt_mean_lev1_', num2str(ii));
a=[a, eval(Var)];
end
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Sulaymon Eshkabilov
Sulaymon Eshkabilov 2021-8-4
Pl., post your question in a sperate thread with some details.
Rik
Rik 2021-8-4
Ran in:
In the screenshot you can see the number of elements of each element. Growing the array dynamically like this (instead of pre-allocating) results in terrible performance. I would also refrain from teaching people to use eval as the solution. As already evidenced in this thread, that is a source of trouble.
k=500000;N=100;%N=348 takes mare than the 55 second limit
tic
a = [];
for ii=1:N
a=[a, rand(k,1)];
end
toc
Elapsed time is 15.427005 seconds.
tic
a = zeros(k,N);
for ii=1:N
a(:,ii)=rand(k,1);
end
toc
Elapsed time is 0.513869 seconds.

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更多回答（2 个）

CARLOTTA DENTICO
CARLOTTA DENTICO 2021-8-4
Do you mean here?
Basically, these are monthly mean of temperature spatially averaged over a specific area of the world, in every months for 29 years (I have a total of 348 means i.e 12x29) that I have extracted from a NetCDf file..
I need these means since I need to calculate time series of winter months (from October to April) and summers months (from May to September) and calculate the mean of winters and summers over 29 years.
All that is to calculate the anomalies of a single month compared to winters in the whole period..
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Sulaymon Eshkabilov
Sulaymon Eshkabilov 2021-8-4
I meant a separate thread and not here. Two questions in one thread that is confusing.

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Rik
Rik 2021-8-4
You should not name your variables dynamically. Why are you not storing them in an array when reading? What is wrong with the code below?
lon = ncread('topaz_V4_myocean_arctic_grid1to8_da_class1_19910115.nc', 'longitude');
lat = ncread('topaz_V4_myocean_arctic_grid1to8_da_class1_19910115.nc', 'latitude');
fram = (lon>=0 & lon<=20 & lat>=76 & lat<=80);
pt_lev1_=zeros(size(pt_lev1,1)*size(pt_lev1,2),348);
for k = 1:348
pt_lev1_(:,k) = reshape(pt_lev1(:,:,k),[],1);
end
pt_mean_lev1_=mean(pt_lev1_(fram,1:k),1,'omitnan')

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