Hello Karena,
dat <- as.data.frame(matrix(sample(0:2, 4000000, replace = TRUE), ncol = 4000))
# if it is a data frame and has to stay that way
# the option that comes to mind is apply()
apply(dat, 2, function(x) {ifelse(x==2, 1, x)})
# if it can be or can be converted to a matrix
dat2 <- as.matrix(dat)
dat2[dat2 == 2] <- 1
On my system, the times for each method were:
> system.time(apply(dat, 2, function(x) {ifelse(x==2, 1, x)}))
user system elapsed
5.472 0.296 6.803
> system.time(dat2[dat2 == 2] <- 1)
user system elapsed
0.584 0.136 0.763
Hope that helps,
Josh
On Wed, Sep 8, 2010 at 1:48 PM, karena <dr.jz...@gmail.com> wrote:
>
> I have a data.frame as follows:
> v1 v2 v3 v4 v5.....v100
> 1 1 0 0 1 2
> 2 1 2 1 0 1
> 1 1 1 2 1 0
> . . . . . .
> . . . . . .
> 1 2 2 1 1 0
>
> so for this data set, what I wanna do is to replace all the '2' with '1',
> how can I do it in an efficient way?
>
> thank you,
>
> karena
> --
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--
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/
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