[R] a question about replacing the value in the data.frame

[Joshua Wiley]

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