[R] interpolation

[René Mayer]

My problem is that x values increas with y until some point then the pattern
reverses. The whole line is a kind of U-shape with a right-buttom to  
middel-top diagonal at the end of it (a look at the plot makes it  
clearer). The interpolation (approx, spline) makes a zick-zack aut of  
it. What I need is to interpolate some points and to preserve the shape.

thanks in andvance
René


Zitat von "David Winsemius" <dwinsemius at comcast.net>:

>
> On Jan 11, 2010, at 7:44 AM, René Mayer wrote:
>
>> Dear R-users,
>> I have a complex line by xy-values (ordered by z).
>> And I would like to get interpolated y-values on the positions of x = 0:600.
>> How do I get the correct points?
>>
>> x=c(790,790,790,790,790,786,783,778,778,766,763,761,761,761,715,628,521,350,160,134,134,129,108,101,93,111,161,249,288,243,139,45,7)
>>
>> y=c(606,606,606,606,606,612,617,627,627,640,641,641,641,641,689,772,877,1048,1240,1272,1272,1258,1242,1239,1239,1214,1122,959,770,479,273,133,45)
>>
>> z=c(0,29,58,87,116,145,174,203,232,261,290,319,348,377,406,435,464,493,522,551,580,609,638,667,696,725,754,783,812,841,870,899,928)
>>
>>
>> plot(y,x,type="b")
>
> That would plot x as a function of y (the reverse of the usual  
> convention. Is that what you want. If so, then the statement that  
> these are ordered by z is misleading. Ordering by z would suggest  
> that each series is a function of z. What sort of interpolation do  
> you want and in how many dimensions?
>
>>
>> # this fails ?????
>> lines(approx(y,x),col="blue") # with xout = c(0:600)
>>
>> thanks in advance,
>> René
>>
>>
>>
>> -- 
>> Dr. rer. nat. Dipl.-Psych. René Mayer
>>
>> Dresden University of Technology
>> Department of Psychology
>> Zellescher Weg 17
>> D-01062 Dresden
>>
>> Tel.: +49-351-4633-4568
>>
>> Email: mayer at psychologie.tu-dresden.de
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>