[R] Beginners Question

[Thomas Zastrow]

Dear all,

I'm completely new to R and at first I must say that it is a great program!

But I have a problem with the function isoMDS from the MASS package. I 
have this code which I load with source() from a file:

x <- c(163.59514923926784, 150.01448475257115, ...... {here are some 
more values})
x.sort <- sort(x)
x.dist <- dist(x.sort)
library(MASS)
x.mds <- isoMDS(x.dist)
plot(x.mds$points, type="n")
text(x.mds$points, labels=as.character("x"))

The problem is in the line where the isoMDS function is applied: I got 
the error:

Fehler in isoMDS(x.dist) : zero or negative distance between objects 9 
and 10

When I look at values 8 and 9 of x.dist, I see that they have the same 
values (I'm not wrong, it's values of 8 and 9 and not 9 and 10):

x.dist[8:9]
[1] 39.8214  39.8214

So, just to give'm a try, I changed the value of x.dist[8]:

x.dist[8] <- c(39.7)

Now, there are defintitely different values in this part of x.dist:

x.dist[7:10]
[1] 39.69898     39.70000      39.82140      39.98892

But when I start isoMDS again, I got again the error:

x.mds <- isoMDS(x.dist)
Fehler in isoMDS(x.dist) : zero or negative distance between objects 9 
and 10


So, where's my error?

Thank you!

Best,

Tom


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