R help - Sep 2010 - a question about replacing the value in the data.frame

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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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.jzhou at 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
> --
> View this message in context:
http://r.789695.n4.nabble.com/a-question-about-replacing-the-value-in-the-data-frame-tp2532010p2532010.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
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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.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

Thanks a lot!
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