[R] Beginners Question

[Thomas Zastrow]

Thank you very much for your answer.

Isn't it possible to tell the isoMDS function that it should ignore 
doubled values with the same value? Or is there a possible to delete all 
the doubled values from the x.dist?

Best regards,

Tom


Prof Brian Ripley schrieb:
> That two distances are the same is *not* what the message says.
>
> You can't just look at elements of the results of dist() and simply 
> relate them back to object numbers.  Try as.matrix(x.dist) for a 
> human-readable form.
>
>

> On Fri, 1 Jun 2007, Thomas Zastrow wrote:
>
>> 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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