R help - Jun 2006 - numeric variables converted to character when recoding missing values

Dear R helpers,

I have a data frame where missing values for numeric variables are coded as
999. I want to recode those as NAs. The following only partially succeeds
because numeric variables are converted to character in the process:

df <- data.frame(a=c(999,1,999,2), b=LETTERS[1:4])
is.na(df[2,1]) <- TRUE
df

    a b
1 999 A
2  NA B
3 999 C
4   2 D

is.numeric(df$a)
[1] TRUE


is.na(df[!is.na(df) & df==999]) <- TRUE
df
     a b
1 <NA> A
2    1 B
3 <NA> C
4    2 D

is.character(df$a)
[1] TRUE

My question is how to do the recoding while avoiding this undesirable side
effect. I'm using R 2.2.1 (yes, I know 2.3.1 is available but don't want
to
switch mid project). I'd appreciate any help.

Further details:

platform i386-pc-mingw32
arch     i386           
os       mingw32        
system   i386, mingw32  
status                  
major    2              
minor    2.1            
year     2005           
month    12             
day      20             
svn rev  36812          
language R              



Juan Pablo Lewinger
Department of Preventive Medicine 
Keck School of Medicine 
University of Southern California

Please read section 2.5 of "An Introduction to R". Numerical missing
values
are assigned as NA:

x[x==999]<-NA

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Juan 
> Pablo Lewinger
> Sent: Friday, June 23, 2006 3:00 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] numeric variables converted to character when 
> recoding missingvalues
> 
> Dear R helpers,
> 
> I have a data frame where missing values for numeric 
> variables are coded as
> 999. I want to recode those as NAs. The following only 
> partially succeeds
> because numeric variables are converted to character in the process:
> 
> df <- data.frame(a=c(999,1,999,2), b=LETTERS[1:4])
> is.na(df[2,1]) <- TRUE
> df
> 
>     a b
> 1 999 A
> 2  NA B
> 3 999 C
> 4   2 D
> 
> is.numeric(df$a)
> [1] TRUE
> 
> 
> is.na(df[!is.na(df) & df==999]) <- TRUE
> df
>      a b
> 1 <NA> A
> 2    1 B
> 3 <NA> C
> 4    2 D
> 
> is.character(df$a)
> [1] TRUE
> 
> My question is how to do the recoding while avoiding this 
> undesirable side
> effect. I'm using R 2.2.1 (yes, I know 2.3.1 is available but 
> don't want to
> switch mid project). I'd appreciate any help.
> 
> Further details:
> 
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    2              
> minor    2.1            
> year     2005           
> month    12             
> day      20             
> svn rev  36812          
> language R              
> 
> 
> 
> Juan Pablo Lewinger
> Department of Preventive Medicine 
> Keck School of Medicine 
> University of Southern California
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! 
> http://www.R-project.org/posting-guide.html
>