HI,
CPU time used:
n<-1e6
system.time({
set.seed(1)
dat1<-data.frame(col1=sample(1:5,n,replace=TRUE))
getcol2<-function(dat1){
dat1$col2[dat1$col1<=2]="L"
dat1
}
dat1<-getcol2(dat1)
})
#user system elapsed
# 0.096 0.000 0.095
system.time({
set.seed(1)
dat1<-data.frame(col1=sample(1:5,n,replace=TRUE))
dat2<-within(dat1,{col2<-ifelse(col1<=2,"L",NA)})
})
# user system elapsed
# 0.580 0.012 0.593
library(car)
system.time({
set.seed(1)
dat1<-data.frame(col1=sample(1:5,n,replace=TRUE))
x<-dat1$col1
dat1$col2<-recode(x,'0="L";1="L";2="L"')
})
#user system elapsed
# 0.548 0.004 0.553
A.K.
----- Original Message -----
From: Sachinthaka Abeywardana <sachin.abeywardana at gmail.com>
To: jim holtman <jholtman at gmail.com>
Cc: r-help at r-project.org
Sent: Monday, August 13, 2012 9:30 PM
Subject: Re: [R] pass by reference
Think you are missing the point, assigning the value back is the same as
passing by value. This is rather inefficient if you ever have to deal with
large datasets. You dont want to keep having a local copy within the scope
of the function and then copying over the original.
On Tue, Aug 14, 2012 at 11:25 AM, jim holtman <jholtman at gmail.com> wrote:
> The assign the value back to the object:
>
> > data<-data.frame(col1=c(1,2,3,4,5))
> >
> > getcol2<-function(data){
> + data$col2[data$col1<=2]="L"
> + data # return value
> + }
> >
> > data <- getcol2(data) # save the return value
> > data
> col1 col2
> 1 1 L
> 2 2 L
> 3 3 <NA>
> 4 4 <NA>
> 5 5 <NA>
> >
>
>
> On Mon, Aug 13, 2012 at 9:23 PM, Sachinthaka Abeywardana
> <sachin.abeywardana at gmail.com> wrote:
> > Hi Jim, R,
> >
> > What you just showed me simply prints out the 2nd column. If you inspect
> > your original data, it still just has 1 column. So its still passing by
> > value.
> >
> > Thanks,
> > Sachin
> >
> > On Tue, Aug 14, 2012 at 11:19 AM, jim holtman <jholtman at gmail.com>
> wrote:
> >>
> >> You have to return the value of 'data' from the function. Functions
> >> do not have "side effects".
> >>
> >> > data<-data.frame(col1=c(1,2,3,4,5))
> >> >
> >> > getcol2<-function(data){
> >> + data$col2[data$col1<=2]="L"
> >> + data # return value
> >> + }
> >> >
> >> > getcol2(data)
> >> col1 col2
> >> 1 1 L
> >> 2 2 L
> >> 3 3 <NA>
> >> 4 4 <NA>
> >> 5 5 <NA>
> >> >
> >>
> >>
> >> On Mon, Aug 13, 2012 at 9:08 PM, Sachinthaka Abeywardana
> >> <sachin.abeywardana at gmail.com> wrote:
> >> > Hi all,
> >> >
> >> > I want to do the following:
> >> >
> >> > data<-data.frame(col1=c(1,2,3,4,5))
> >> >
> >> > getcol2<-function(data){
> >> > data$col2[data$col1<=2]="L"
> >> > }
> >> >
> >> > getcol2(data)
> >> >
> >> > Unfortunately in the above col2 does not appear in the final data. So
> >> > how
> >> > would you pass this by reference such that you would get it back?
> >> >
> >> > Thanks,
> >> > Sachin
> >> >
> >> > [[alternative HTML version deleted]]
> >> >
> >> > ______________________________________________
> >> > R-help at 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.
> >>
> >>
> >>
> >> --
> >> Jim Holtman
> >> Data Munger Guru
> >>
> >> What is the problem that you are trying to solve?
> >> Tell me what you want to do, not how you want to do it.
> >
> >
>
>
>
> --
> Jim Holtman
> Data Munger Guru
>
> What is the problem that you are trying to solve?
> Tell me what you want to do, not how you want to do it.
>
[[alternative HTML version deleted]]
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.