If it were just one loop by itself and I was doing the calculation for just one month for all of my 317 stations, I would agree with. However, this function itself is inside another loop which goes through each month and year that I need the calculation for each of the stations.
If you have any suggestions for how I could speed up the loop that is welcome, but I would like to try to remove it given that it is nested inside another loop. A On Wed, Aug 11, 2010 at 2:59 PM, Greg Snow <greg.s...@imail.org> wrote: > What is wrong with using a loop? > > It used to be that loops were much slower than some of the alternatives, > but now days a well crafted loop runs almost as fast (sometime faster) than > the apply functions. So if the loop is working for you, use it and don't > worry about it (though there may be ways to speed up the loop). > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > greg.s...@imail.org > 801.408.8111 > > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r- > > project.org] On Behalf Of Adrienne Wootten > > Sent: Wednesday, August 11, 2010 10:36 AM > > To: r-help@r-project.org > > Subject: [R] Running something without a loop when the result from the > > previous iteration is require for the current iteration > > > > Hello Everyone! > > > > Here's what I'm trying to do. I'm working on generating occurrences of > > precipitation based upon precipitation occurrence for a station during > > the > > previous day and two stations that have already been generated by joint > > probablities and 1st order Markov chains or by the same generation > > process. > > This has to be done for each remaining stations for each month. > > > > > genmat # 7 stations in this example, line_before is the climatology > > of the > > last day of the previous month. Stations 4 and 6 have been generated > > already > > in this example > > [,1] [,2] [,3] [,4] [,5] [,6] [,7] > > line_before 1 1 1 0 1 1 1 > > NA NA NA 1 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 1 NA 0 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 1 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 0 NA 0 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 1 NA 1 NA > > NA NA NA 0 NA 0 NA > > > num # station to generate > > [1] 2 > > > use1 # 1st station to use in generation > > [1] 6 > > > use2 # 2nd station to use in generation > > [1] 4 > > > > > genmat = event.gen2(genmat,use1,use2,num,ortho_obs_used) # Generation > > function shown below > > > genmat # genmat - after it has gone through station 2 > > [,1] [,2] [,3] [,4] [,5] [,6] [,7] > > line_before 1 1 1 0 1 1 1 > > NA 0 NA 1 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 1 NA 0 NA > > NA 1 NA 1 NA 1 NA > > NA 1 NA 1 NA 1 NA > > NA 1 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 1 NA 1 NA 1 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 1 NA 1 NA 1 NA > > NA 0 NA 0 NA 0 NA > > NA 1 NA 1 NA 1 NA > > NA 0 NA 1 NA 1 NA > > NA 1 NA 1 NA 1 NA > > NA 0 NA 0 NA 0 NA > > NA 1 NA 0 NA 1 NA > > NA 0 NA 0 NA 0 NA > > NA 0 NA 0 NA 0 NA > > NA 1 NA 1 NA 1 NA > > NA 1 NA 1 NA 1 NA > > NA 1 NA 1 NA 1 NA > > NA 0 NA 0 NA 0 NA > > > > Where event.gen2 is this function: > > > > event.gen2 = function(genmat,use1,use2,num,ortho_obs_used){ > > > > for(r in 2:nrow(genmat)){ > > > > ran = runif(1,0,1) > > > > if(genmat[r,use1]==0 & genmat[r,use2]==0){ > > genmat[r,num]<-ifelse(genmat[r- > > 1,num]==0,ifelse(ran<ortho_obs_used$Pr[1],1,0),ifelse(ran<ortho_obs_use > > d$Pr[4],1,0)) > > } > > > > if(genmat[r,use1]==0 & genmat[r,use2]==1){ > > genmat[r,num]<-ifelse(genmat[r- > > 1,num]==0,ifelse(ran<ortho_obs_used$Pr[2],1,0),ifelse(ran<ortho_obs_use > > d$Pr[5],1,0)) > > } > > > > if(genmat[r,use1]==1 & genmat[r,use2]==0){ > > genmat[r,num]<-ifelse(genmat[r- > > 1,num]==0,ifelse(ran<ortho_obs_used$Pr[3],1,0),ifelse(ran<ortho_obs_use > > d$Pr[7],1,0)) > > } > > > > if(genmat[r,use1]==1 & genmat[r,use2]==1){ > > genmat[r,num]<-ifelse(genmat[r- > > 1,num]==0,ifelse(ran<ortho_obs_used$Pr[6],1,0),ifelse(ran<ortho_obs_use > > d$Pr[8],1,0)) > > } > > > > gc() > > } > > > > genmat > > > > } > > > > #### > > > > ortho_obs_used is a data frame that contains the probablity of > > precipitation > > occurring on a given day for a specific set of condtions. > > For instance ortho_obs_used$Pr[1] is the probablity of rain at station > > s for > > day d, given that there was no rain at station s for day d-1 and no > > rain at > > either of the other two stations for day d. > > > > The event.gen2 function handles the generation, and it runs quickly for > > the > > 5 remaining stations and one month, but I have to run this for 317 > > stations > > over 48 months or more, and it becomes a really bad bottleneck. So > > what I'd > > like to know is if there is anyway that I can re-write this function to > > work > > without a loop. I couldn't find anything from previous posts about > > getting > > out of loops where the previous iteration is required to determine the > > next > > calculation. > > > > Sorry for the length of the post, but I thought it best to try to > > explain > > what I was doing first, before diving into my question > > > > Thanks in advance! > > > > Adrienne Wootten > > Graduate Research Assistant/Environmental Meteorologist > > M.S. Atmospheric Science > > NC State University > > State Climate Office of North Carolina > > Raleigh, NC 27695 > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-help@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide http://www.R-project.org/posting- > > guide.html > > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
