[R] loop is going to take 26 hours - needs to be quicker!

[Rainer M Krug]

Jenny Barnes wrote:
> Dear R-help,
> 
> I have a loop, which is set to take about 26 hours to run at the rate it's going 
> - this is ridiculous and I really need your help to find a more efficient way of 
> loading up my array gpcc.array:
> 
> #My data is stored in a table format with all the data in one long column 
> #running though every longitute, for every latitude, for every year. The 
> #original data is sotred as gpcc.data2 where dim(gpcc.data2) = [476928,5] where 
> #the 5th column is the data:
> 
> #make the array in the format I need [longitude,latitude,years]
> 
> gpcc.array <- array(NA, c(144,72,46)) 
> 
> n=0
> for(k in 1:46){
> for(j in 1:72){
> for(i in 1:144){
> n <- n+1
> gpcc.array[i,j,k] <- gpcc.data2[n,5]
> print(j)
> }
> }
> }

I don't know if it is faster - but adding three columns to qpcc.data, 
one for longitude, one for lattitude and one for year (using rep() as 
they are in sequence) and the using reshape() might be faster?


> 
> So it runs through all the longs for every lat for every year - which is the 
> order the data is running down the column in gpcc.data2 so n increses by 1 each 
> time and each data point is pulled off....
> 
> It needs to be a lot quicker, I'd appreciate any ideas!
> 
> Many thanks for taking time to read this,
> 
> Jenny Barnes
> 
> ~~~~~~~~~~~~~~~~~~
> Jennifer Barnes
> PhD student - long range drought prediction
> Climate Extremes
> Department of Space and Climate Physics
> University College London
> Holmbury St Mary, Dorking
> Surrey
> RH5 6NT
> 01483 204149
> 07916 139187
> Web: http://climate.mssl.ucl.ac.uk
> 
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> and provide commented, minimal, self-contained, reproducible code.


-- 
Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation
Biology (UCT)

Department of Conservation Ecology and Entomology
University of Stellenbosch
Matieland 7602
South Africa

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email:	RKrug at sun.ac.za
       	Rainer at krugs.de