[R] tree error

[Robert Schilling Schick]

Hi- I'm trying to run a classification tree, and have received an error 
I'm unfamiliar with. Following is the R code, and the first 10 lines of 
my matrix. Any help would be appreciated.

> kuv.tree <- read.table("kuv3_mantelmatrix.txt",header=T,sep="\t")
> library(tree)
> attach(kuv.tree)
> ktree <- tree(Species ~ Drig + dwellln, data=kuv.tree)
Error in arg == choices : comparison (1) is possible only for vector types

Number	Species	Drig	DShore	dwellln	Depth	X	Y
1	0	26019.2	32311	10.1666	-20.5872	47528.1	-20268.2
2	0	28284.3	36400.6	10.2501	-24.5176	49528.1	-15268.2
3	0	51312.8	71175.8	10.8457	-95.3488	49528.1	23731.8
4	0	33615.5	16643.3	10.4227	-1.61133	50528.1	-36268.2
5	0	16643.3	7615.77	9.71976	-11.6917	12528.1	-33268.2
6	0	23409.4	22360.7	10.0609	-23.4709	-471.875	-11268.2
7	0	55226.8	48301.1	10.9192	-21.0988	-15471.9	21731.8
8	0	23706.5	25495.1	10.0735	-20.2442	528.125	-8268.24
9	0	8485.3	22825.4	9.04609	-24.7801	27528.1	-25268.2
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