Hi
why do you insist on loops. R is not C. If you want to use loops use C or
similar programming languages. It is almost always better to apply whole
object approach. Kind and clever people already programmed it (sometimes
in C ).
x<-rnorm(20)
x[c(10,12,13,17)]<-NA
x
[1] -1.12423790 0.80641765 -1.02686262 0.71894420 -0.76157153
-0.09612362
[7] 0.36681907 0.11164870 -1.06308689 NA -1.32903523 NA
[13] NA 0.43308928 -0.16599726 -1.85594816 NA
0.02117957
[19] -0.58170838 1.45417843
library(zoo)
na.locf(x)
[1] -1.12423790 0.80641765 -1.02686262 0.71894420 -0.76157153
-0.09612362
[7] 0.36681907 0.11164870 -1.06308689 -1.06308689 -1.32903523
-1.32903523
[13] -1.32903523 0.43308928 -0.16599726 -1.85594816 -1.85594816
0.02117957
[19] -0.58170838 1.45417843
Would be always quicker then for cycle with condition checked in each
step.
There was an article in R News and P.Burns R inferno is also worth to look
at if you are interested in loop performance.
If you want to see where the time is spent use Rprof
Regards
Petr
siddharth.gar...@gmail.com napsal dne 28.07.2010 15:20:11:
> Thanks for the reply Petr. I have solved this problem using sapply but
what I
> am trying to understand here is, why this code is slow.
>
> One of the possible reasons could be when I use the assignment operator
ie
> D$x[i]=D$x[i-1]
> It actually makes a new copy of D$x with the modified value.
>
> Another reason could be indexed lookups might not be very fast in R.
>
> Regards
> Siddharth
>
>
>
> ------Original Message------
> From: Petr PIKAL
> To: siddharth.gar...@gmail.com
> Cc: r-help@r-project.org
> Subject: Odp: [R] Data frame modification
> Sent: Jul 28, 2010 6:15 PM
>
> Hi
>
> r-help-boun...@r-project.org napsal dne 28.07.2010 11:30:48:
>
> > Hi
> >
> > I am trying to modify a data frame D with lists x and y in such a way
> that if
> > a value in x==0 then it should replace that value with the last not
zero
> valuein x. I.e.
> >
> > for loop over i{
> > if(D$x[i]==0)
> > D$x[i]=D$x[i-1]
> > }
> >
> > The data frame is quite large in size ~ 43000 rows. This operation is
> taking a
> > large amount of time. Can someone please suggest me what might be the
> reason.
>
> Bad programming practice? I would suggest to use zoo package and na.locf
> function after changing all zero values to NA.
>
> Regards
> Petr
>
> >
> > Thanks
> > Regards
> > Siddharth
> > Sent on my BlackBerry® from Vodafone
> > ______________________________________________
> > 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.
>
>
>
> Sent on my BlackBerry® from Vodafone
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