R help - May 2009 - predict function the other way around

Dear List,
Consider the following example

x=c(1,2,3,4,5)
y=c(2,4,6,8,10)
linearmodel=lm(y~x)

To predict a y-value if you know the corresponding x value is very easy 
with the command predict.

predict(linearmodel, newdata=(x=1.5))

The other way around, to predict an x-value with a corresponding 
y-value, doesn't work unfortunately.
Is there another function that can do that, or do I need to solve that 
problem the classical way?

Thanks in advance

Gerrit Voigt

Why not use the x=T and y=T paramemters and see if :

linearmodel=lm(y~x, x=T, y=T)linearmodel$model
(linearmodel$model)
    y x
1  2 1
2  4 2
3  6 3
4  8 4
5 10 5

.... give you useful results. If you want to interpolate or  
extrapolate, then search for threads regarding those tasks.

-- 
David Winsemius
On May 11, 2009, at 11:20 AM, Gerrit Voigt wrote:
> Dear List,
> Consider the following example
>
> x=c(1,2,3,4,5)
> y=c(2,4,6,8,10)
> linearmodel=lm(y~x)
>
> To predict a y-value if you know the corresponding x value is very  
> easy with the command predict.
>
> predict(linearmodel, newdata=(x=1.5))
>
> The other way around, to predict an x-value with a corresponding y- 
> value, doesn't work unfortunately.
> Is there another function that can do that, or do I need to solve  
> that problem the classical way?
>
> Thanks in advance
>
> Gerrit Voigt
>
> ______________________________________________
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT