R help - Jul 2010 - how to collapse categories or re-categorize variables?

I am sure this is a very basic question:

I have 600,000 categorical variables in a data.frame - each of which is
classified as "0", "1", or "2"

What I would like to do is collapse "1" and "2" and leave
"0" by itself,
such that after re-categorizing "0" = "0"; "1" =
"1" and "2" = "1" --- in
the end I only want "0" and "1" as categories for each of
the variables.

Also, if possible I would rather not create 600,000 new variables, if I can
replace the existing variables with the new values that would be great!

What would be the best way to do this?

Thank you!


-- 
Thanks,
CC

	[[alternative HTML version deleted]]

Do you want to replace specific values of a data set?

df <- sample(c(0,1,2),600,replace=T)
table(df)
df[df==2]<-1
table(df)

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Hi:

See ? levels. Here's a toy example:
> x <- factor(sample(0:2, 10, replace = TRUE))
> x
 [1] 1 2 1 0 2 2 2 2 2 1
Levels: 0 1 2
> levels(x) <- c(0, 1, 1)    # Change level 2 to 1
> x
 [1] 1 1 1 0 1 1 1 1 1 1
Levels: 0 1

HTH,
Dennis


On Fri, Jul 16, 2010 at 10:18 AM, CC <turtysmail@gmail.com> wrote:
> I am sure this is a very basic question:
>
> I have 600,000 categorical variables in a data.frame - each of which is
> classified as "0", "1", or "2"
>
> What I would like to do is collapse "1" and "2" and
leave "0" by itself,
> such that after re-categorizing "0" = "0";
"1" = "1" and "2" = "1" --- in
> the end I only want "0" and "1" as categories for each
of the variables.
>
> Also, if possible I would rather not create 600,000 new variables, if I can
> replace the existing variables with the new values that would be great!
>
> What would be the best way to do this?
>
> Thank you!
>
>
> --
> Thanks,
> CC
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> 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.
>
	[[alternative HTML version deleted]]

Hi,
On Fri, Jul 16, 2010 at 5:18 PM, CC <turtysmail at gmail.com>
wrote:
> I am sure this is a very basic question:
>
> I have 600,000 categorical variables in a data.frame - each of which is
> classified as "0", "1", or "2"
>
> What I would like to do is collapse "1" and "2" and
leave "0" by itself,
> such that after re-categorizing "0" = "0";
"1" = "1" and "2" = "1" --- in
> the end I only want "0" and "1" as categories for each
of the variables.
Something like this should work

for (i in names(dat)) {
dat[, i]  <- factor(dat[, i], levels = c("0", "1",
"2"), labels c("0", "1", "1))
}

-Ista
>
> Also, if possible I would rather not create 600,000 new variables, if I can
> replace the existing variables with the new values that would be great!
>
> What would be the best way to do this?
>
> Thank you!
>
>
> --
> Thanks,
> CC
>
> ? ? ? ?[[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.
>


-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org