R help - Oct 2008 - using ifelse with surprising results

Thanks for the gracious assistance in advance

I'm working on a non-metric scaling problem and am calculating the distance
for input to isoMDS

Here is the code

library(MASS)
vegdata <- tapply(Percent, list(PRIMARY_VE, MASTERID), sum)
x.mat <- matrix(x, nrow=40, ncol=2750, byrow=TRUE, dimnames c(dimnames(x)[1],
dimnames(x)[2]))


 vegdata.dd <- dist(x)
 vegdata.dd <- ifelse(vegdata.dd==NA, 0.01, x.dd)
  vegdata.dd

Everything works as expected until I try to replace the NA values in the
distance matrix.
the ifelse statement converts the entire dataset to NA.

What am I doing incorrectly?

Once again, Thanks

Steve


Steve Friedman Ph. D.
Spatial Statistical Analyst
Everglades and Dry Tortugas National Park
950 N Krome Ave (3rd Floor)
Homestead, Florida 33034

Office (305) 224 - 4282
Steve_Friedman at nps.gov

Try the following instead:

vegdata.dd[is.na(vegdata.dd)] <- 0.01

-Christos
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of 
> Steve_Friedman at nps.gov
> Sent: Friday, October 17, 2008 4:50 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] using ifelse with surprising results
> 
> 
> Thanks for the gracious assistance in advance
> 
> I'm working on a non-metric scaling problem and am 
> calculating the distance for input to isoMDS
> 
> Here is the code
> 
> library(MASS)
> vegdata <- tapply(Percent, list(PRIMARY_VE, MASTERID), sum) 
> x.mat <- matrix(x, nrow=40, ncol=2750, byrow=TRUE, dimnames = 
> c(dimnames(x)[1], dimnames(x)[2]))
> 
> 
>  vegdata.dd <- dist(x)
>  vegdata.dd <- ifelse(vegdata.dd==NA, 0.01, x.dd)
>   vegdata.dd
> 
> Everything works as expected until I try to replace the NA 
> values in the distance matrix.
> the ifelse statement converts the entire dataset to NA.
> 
> What am I doing incorrectly?
> 
> Once again, Thanks
> 
> Steve
> 
> 
> Steve Friedman Ph. D.
> Spatial Statistical Analyst
> Everglades and Dry Tortugas National Park 950 N Krome Ave 
> (3rd Floor) Homestead, Florida 33034
> 
> Office (305) 224 - 4282
> Steve_Friedman at nps.gov
> 
> ______________________________________________
> 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.
> 
>

On Fri, Oct 17, 2008 at 3:50 PM,  <Steve_Friedman at nps.gov>
wrote:
>
> Thanks for the gracious assistance in advance
>
> I'm working on a non-metric scaling problem and am calculating the
distance
> for input to isoMDS
>
> Here is the code
>
> library(MASS)
> vegdata <- tapply(Percent, list(PRIMARY_VE, MASTERID), sum)
> x.mat <- matrix(x, nrow=40, ncol=2750, byrow=TRUE, dimnames >
c(dimnames(x)[1], dimnames(x)[2]))
>
>
>  vegdata.dd <- dist(x)
>  vegdata.dd <- ifelse(vegdata.dd==NA, 0.01, x.dd)
>  vegdata.dd
>
> Everything works as expected until I try to replace the NA values in the
> distance matrix.
> the ifelse statement converts the entire dataset to NA.
>
> What am I doing incorrectly?
What does NA == NA equal?  This is not intuitive (at first!) but very
important when dealing with NAs.

Hadley

-- 
http://had.co.nz/