[R] approxfun-problems (yleft and yright ignored)

[Samuel Wuest]

Hi Martin,

indeed, as mentioned in the bug-report, the results are inconsistent,
and each time I rerun, I get different results... Sometimes, the range
is correct even on my machine, but mostly I get values >1 back:

Here is another run:
> ### load the data: a list called approx.data
>  load(file="approx.data.Rdata")
> ### contains the slots "x", "y", "input"
> names(approx.data)
[1] "x"     "y"     "input"
> ### with y ranging between 0 and 1
....
> ### generate the interpolation function (warning message benign)
> interp <- approxfun(approx.data$x, approx.data$y, yleft=1, yright=0, rule=2)
Warning message:
In approxfun(approx.data$x, approx.data$y, yleft = 1, yright = 0,  :
  collapsing to unique 'x' values
> ### apply to input-values
> y.out <- interp(approx.data$input)
>
> ### still I find output values >1, even though yleft=1:
> range(y.out)
[1]  -1.360612e+81  2.151192e+249
....
This script was run on the same machine, same R-version ect.
this demonstrates the issue again, and when running the script again
before the bug-report, I had overlooked, that the range was indeed
correct...

I guess Greg Snow had suggested a fix for the bug correctly and the
issue should be resolved as posted by Duncan Murdoch. Thanks a
million!!

Best, Sam


On 11 September 2010 15:53, Martin Maechler <maechler at stat.math.ethz.ch> wrote:
>>>>>> "MM" == Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>>     on Sat, 11 Sep 2010 16:04:37 +0200 writes:
>
>>>>>> "SW" == Samuel Wuest <wuests at tcd.ie>
>>>>>>     on Thu, 26 Aug 2010 14:34:26 +0100 writes:
>
>    SW> Hi Greg,
>    SW> thanks for the suggestion:
>
>    SW> I have attached some small dataset that can be used to reproduce the
>    SW> odd behavior of the approxfun-function.
>
>    SW> If it gets stripped off my email, it can also be downloaded at:
>    SW> http://bioinf.gen.tcd.ie/approx.data.Rdata
>
>    SW> Strangely, the problem seems specific to the data structure in my
>    SW> expression set, when I use simulated data, everything worked fine.
>
>    SW> Here is some code that I run and resulted in the strange output that I
>    SW> have described in my initial post:
>
>    >>> ### load the data: a list called approx.data
>    >>> load(file="approx.data.Rdata")
>    >>> ### contains the slots "x", "y", "input"
>    >>> names(approx.data)
>    SW> [1] "x"     "y"     "input"
>    >>> ### with y ranging between 0 and 1
>    >>> range(approx.data$y)
>    SW> [1] 0 1
>    >>> ### compare ranges of x and input-x values (the latter is a small subset of 500 data points):
>    >>> range(approx.data$x)
>    SW> [1] 3.098444 7.268812
>    >>> range(approx.data$input)
>    SW> [1]  3.329408 13.026700
>    >>>
>    >>>
>    >>> ### generate the interpolation function (warning message benign)
>    >>> interp <- approxfun(approx.data$x, approx.data$y, yleft=1, yright=0, rule=2)
>    SW> Warning message:
>    SW> In approxfun(approx.data$x, approx.data$y, yleft = 1, yright = 0,  :
>    SW> collapsing to unique 'x' values
>    >>>
>    >>> ### apply to input-values
>    >>> y.out <- sapply(approx.data$input, interp)
>    >>>
>    >>> ### still I find output values >1, even though yleft=1:
>    >>> range(y.out)
>    SW> [1] 0.000000 7.207233
>
>
>    MM> I get completely different (and correct) results,
>    MM> by the way the *same* you have in the bug report you've
>    MM> submitted
>    MM> (https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=14377)
>    MM> and which does *not* show any bug:
>
>    >> range(y.out)
>    MM> [1] 0.0000000 0.9816907
>
>    MM> Of course, I do believe that you've seen the above problems,
>    MM> -- on 64-bit Mac ? as you report in sessionInfo() ? --
>    MM> but I cannot reproduce them.
>
>    MM> And also, you seem yourself to be able to get different results
>    MM> for the same data... what are the circumstances?
>
> I now see that you *did* mention the fact that you
> see *different* results when you *RE*run the same code
> on this data.
> The subject (" ...yleft and yright ignored") is misleading in
> any case.  These are not at all ignored...,
> but indeed (as Duncan Murdoch has noted on the bug website),
> there *is* a bug,
> so you are principally right in reporting -- thank you!
> ....
> and I could also confirm that -- as you mentioned in your first
> post -- this bug does not appear when using R 2.8.1 (at least on
> my platform).
>
> Martin
>
>



-- 
-----------------------------------------------------
Samuel Wuest
Smurfit Institute of Genetics
Trinity College Dublin
Dublin 2, Ireland
Phone: +353-1-896 2444
Web: http://www.tcd.ie/Genetics/wellmer-2/index.html
Email: wuests at tcd.ie