R help - Feb 2012 - Error in apply(x2, 1, diff) : dim(X) must have a positive length

Anyone knows hat might be the cause of this error? Thanks for any help!
>library(MASS)
> dif.mns = function(x2,tr1=.2,tr2=.3){ 
+ #generates four different 'means' using 
+ #difference scores from x2, an n x 2 matrix
+ #for use w/ bootstrap comparisons 
+     diffs = apply(x2,1,diff)  
+     mn1=mean(diffs) 
+     mn2=mean(diffs,tr=.2) 
+     mn3=mean(diffs,tr=.3) 
+     mn4=median(diffs) 
+ mns=c(mn1,mn2,mn3,mn4)  
+ list(mnds=round(mns,3)) } 
> dif.mns(shoes)
Error in apply(x2, 1, diff) : dim(X) must have a positive length

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On Feb 12, 2012, at 7:05 PM, hithit168 wrote:
> Anyone knows hat might be the cause of this error? Thanks for any  
> help!
>
>> library(MASS)
>> dif.mns = function(x2,tr1=.2,tr2=.3){
> + #generates four different 'means' using
> + #difference scores from x2, an n x 2 matrix
> + #for use w/ bootstrap comparisons
> +     diffs = apply(x2,1,diff)
> +     mn1=mean(diffs)
> +     mn2=mean(diffs,tr=.2)
> +     mn3=mean(diffs,tr=.3)
> +     mn4=median(diffs)
> + mns=c(mn1,mn2,mn3,mn4)
> + list(mnds=round(mns,3)) }
>
>> dif.mns(shoes)
> Error in apply(x2, 1, diff) : dim(X) must have a positive length
>
You have given apply a list.

-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

Thank you for your help, David. I was trying to run bootrapping on the
dataset "shoes" from MASS package. But I still have some problem here.
> as.matrix(data.frame(shoes),nrows=10,ncols=2,byrow=T)
A B
[1,] 13.2 14.0
[2,] 8.2 8.8
[3,] 10.9 11.2
[4,] 14.3 14.2
[5,] 10.7 11.8
[6,] 6.6 6.4
[7,] 9.5 9.8
[8,] 10.8 11.3
[9,] 8.8 9.3
[10,] 13.3 13.6
> y=as.matrix(data.frame(shoes),nrows=10,ncols=2,byrow=T)
> class(y)
[1] "matrix"
> apply(y,1,diff)
[1] 0.8 0.6 0.3 -0.1 1.1 -0.2 0.3 0.5 0.5 0.3
> dif.mns <- function(x2,tr1=.1,tr2=.2){
+ diffs=apply(x2,1,diff) 
+ mn1=mean(diffs)
+ mn2=mean(diffs,tr=.1)
+ mn3=mean(diffs,tr=.2)
+ mn4=median(diffs)
+ mns=c(mn1,mn2,mn3,mn4) 
+ list(mnds=round(mns,3))}
> dif.mns(y,tr1=.1,tr2=.2)
$mnds
[1] 0.410 0.400 0.417 0.400
> bootstrap(y,nboot=1000,theta=dif.mns)
Error in apply(x2, 1, diff) : dim(X) must have a positive length

I am not sure what I am doing wrong. When I run apply(y,1,diff) I am able to
get output, and when I run dif.mns with just the original dataset, I am also
able to get output.



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