[R] conditional statement to replace values in dataframe with NA

[Bert Gunter]

Have you read "An Intro to R?" If not,please do so before posting
further. The way you are going about things makes me think you
haven't, but ...

This **is** a slightly tricky application of indexing, if I understand
you correctly. Here are two essentially identical ways to do it, but
the second is a little trickier

## First
> dat1[dat1$x==1 & dat1$y==1,1:2] <- rep(NA,2)
> dat1
     x    y fac
1 <NA> <NA>   A
2    1    2   B
3    1    3   A
4 <NA> <NA>   C
5    1    2   A
6    1    3   C

##Slightly trickier version using with() to avoid explicit extraction
from data frame
## Reconstitute dat1

> dat1
  x y fac
1 1 1   C
2 1 2   C
3 1 3   B
4 1 1   B
5 1 2   C
6 1 3   B

dat1 <- with(dat1,{dat1[x==1 & y==1,1:2] <- rep(NA,2); dat1})
> dat1
     x    y fac
1 <NA> <NA>   B
2    1    2   A
3    1    3   A
4 <NA> <NA>   C
5    1    2   A
6    1    3   B

## ?with for explanation

-- Bert

On Wed, Jun 6, 2012 at 8:58 PM, Daisy Englert Duursma
<daisy.duursma at gmail.com> wrote:
> Hello and thanks for helping.
>
> #some data
> L3 <- LETTERS[1:3]
> dat1 <- data.frame(cbind(x=1, y=rep(1:3,2), fac=sample(L3, 6, replace=TRUE)))
>
>
> #When x==1 and y==1 I want to replace the 1 values with NA
>
> #I can select the rows I want:
> dat2<-subset(dat1,x==1 & y==1)
> #replace the 1 with NA
> dat2$x<-rep(NA,nrow(dat2)
> dat2$y<-rep(NA,nrow(dat2)
>
> #select the other rows and rbind everything back together
> #This is where I get stuck
>
> #The end dataframe will look something like:
>
>   x y  fac
> NA NA   B
> NA NA   A
> 1 2   C
> 1 3   C
> 1 2   C
> 1 3   A
>
> #Is there a better way to do this where I do not need to subset
> perhaps using lapply?
>
>
> Thanks,
> Daisy
>
> --
> Daisy Englert Duursma
> Department of Biological Sciences
> Room E8C156
> Macquarie University, North Ryde, NSW 2109
> Australia
>
> Tel +61 2 9850 9256
>
> ______________________________________________
> R-help at r-project.org mailing list
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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.



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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