R help - Jun 2011 - Replace selected columns of a dataframe with NA

I am using the following command to replace all the missing values and
assorted typos in a dataframe with NA:

mydata[mydata>80]=NA

The problem is that the first column contains values which should be
more than 80, so really I want to do it just for
mydata[,2:length(mydata)]

I can't seem to re-write the code to fit:

mydata[,2:length(mydata)>80]=NA # no error message, but doesn't work-
doesn't do anything, it would seem

I realise I can just keep the first column somewhere safe and copy it
back again when I'm done, but I wondered if there was a more elegant
solution, which would be much more important, if say I just wanted to
replace the odd columns, or something like that.

I found this code on the internet too:

idx <- which(foo>80, arr.ind=TRUE)
foo[idx[1], idx[2]] <- NA

But I can't seem to rewrite that either, for the same reason

Many thanks!

Chris Beeley
Institute of Mental Health

Hi
> 
> I am using the following command to replace all the missing values and
> assorted typos in a dataframe with NA:
> 
> mydata[mydata>80]=NA
> 
> The problem is that the first column contains values which should be
> more than 80, so really I want to do it just for
> mydata[,2:length(mydata)]
> 
> I can't seem to re-write the code to fit:
> 
> mydata[,2:length(mydata)>80]=NA # no error message, but doesn't
work-
> doesn't do anything, it would seem
mydata[,-1][mydata[,-1]>80]<-NA

shall do what you want

Regards
Petr
> 
> I realise I can just keep the first column somewhere safe and copy it
> back again when I'm done, but I wondered if there was a more elegant
> solution, which would be much more important, if say I just wanted to
> replace the odd columns, or something like that.
> 
> I found this code on the internet too:
> 
> idx <- which(foo>80, arr.ind=TRUE)
> foo[idx[1], idx[2]] <- NA
> 
> But I can't seem to rewrite that either, for the same reason
> 
> Many thanks!
> 
> Chris Beeley
> Institute of Mental Health
> 
> ______________________________________________
> 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.

I don't know if you have factors in your data frame, but in any case, 
you can try the following approach:

mydata <- data.frame(id = 1:10, x = rnorm(10, 80),
     z = rnorm(10, 80), w = gl(2, 5))
mydata

f <- function (x) {
     if (is.numeric(x))
         x[x > 80] <- NA
     x
}
mydata[-1] <- lapply(mydata[-1], f)
mydata


I hope it helps.

Best,
Dimitris


On 6/20/2011 10:40 AM, Chris Beeley wrote:
> I am using the following command to replace all the missing values and
> assorted typos in a dataframe with NA:
>
> mydata[mydata>80]=NA
>
> The problem is that the first column contains values which should be
> more than 80, so really I want to do it just for
> mydata[,2:length(mydata)]
>
> I can't seem to re-write the code to fit:
>
> mydata[,2:length(mydata)>80]=NA # no error message, but doesn't
work-
> doesn't do anything, it would seem
>
> I realise I can just keep the first column somewhere safe and copy it
> back again when I'm done, but I wondered if there was a more elegant
> solution, which would be much more important, if say I just wanted to
> replace the odd columns, or something like that.
>
> I found this code on the internet too:
>
> idx<- which(foo>80, arr.ind=TRUE)
> foo[idx[1], idx[2]]<- NA
>
> But I can't seem to rewrite that either, for the same reason
>
> Many thanks!
>
> Chris Beeley
> Institute of Mental Health
>
> ______________________________________________
> 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.
>
-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
Web: http://www.erasmusmc.nl/biostatistiek/