[R-sig-eco] biplot question: "Error in 1L:n : argument of length 0"

[Michael Marsh]

I am trying to obtain biplots of NMDS results, ideally like the 
rpart.pca() result with mvpart.
Can someone easily tell me why I get this error:
Error in 1L:n : argument of length 0
from this script, and graphical output (below) lacking labels for either 
sites or species?
x and y matrices are shown below script.
modifying "y" by removing NaN rows did not change output.
Thanks!,
Mike Marsh
swamp at blarg.net

----------------------
Q.wd<-as.data.frame(read.table(file.choose(),header=T))
 > #text dataset is Q.WD.foliar.revised.txt

 > library(vegan)
 > Q09shrub.min<-vegtab(Q09shrub,min=2)
 > Q09shrub.std<-decostand(Q09shrub.min, method="max")
 > Q09shrub.dist<- dist(Q09shrub.std)
 > Q09shrub.ward<-hclust(Q09shrub.dist,method="ward",members=NULL)
 >  NMDS.Q09shrub<-metaMDS(Q09shrub)

Wisconsin double standardization
Run 0 stress 0.08176961
Run 1 stress 0.1011811
Run 2 stress 0.07507627
... New best solution
... procrustes: rmse 0.04824229  max resid 0.1222105
Run 3 stress 0.1011877
Run 4 stress 0.07507602
... New best solution
... procrustes: rmse 0.0001471213  max resid 0.0002974951
*** Solution reached

 > x<-plot(NMDS.Q09shrub, "sites")
 > y<-plot(NMDS.Q09shrub, "species")
 > biplot(x,y)
Error in 1L:n : argument of length 0
 > ordicluster(NMDS.Q09shrub, Q09shrub.ward)
 >
 > x
$sites
              NMDS1       NMDS2
9Q05-ST -0.7781618 -0.05087985
9Q06-VS  0.6462465 -0.41377399
9Q12-ST -0.3126179 -0.80107514
9Q15ECS -0.8780461  0.20632944
9Q15WST -0.7672079  0.88777750
9Q16-VS  0.8652229  0.56684307
9Q19-ST  0.1374252 -0.41322443
9Q24-ST  0.3140148 -0.12115606
9Q26-ST -1.0044059 -0.15339828
9Q29-DS  0.9608797  0.35394121
9Q33-VS  0.8166505 -0.06138349

$species
NULL

attr(,"class")
[1] "ordiplot"
 > y
$sites
NULL

$species
              NMDS1       NMDS2
ACMA3          NaN         NaN
AMAL2  -0.05672919 -0.81171544
ARRI2   0.84801299  0.24651319
ARTR2  -0.93597835  0.02417604
ARTR4  -1.01337771 -0.05343535
GRSP           NaN         NaN
CHVI8  -0.74187745 -0.02949452
ERBL2          NaN         NaN
ERNA10 -0.61157997  0.47464632
NEST5   0.87499085 -0.04070596
PREM   -0.90401815  1.25730322
PRVI           NaN         NaN
PUTR2   0.16079095 -0.36676073
RICE   -0.35775047 -0.46386377
ROWO           NaN         NaN
SYAL2          NaN         NaN
SYOR2  -0.36836460 -1.13451214

attr(,"class")
[1] "ordiplot"
 >