[R] SDMTools package - calculating overlap?
David Winsemius
dwinsemius at comcast.net
Mon Jul 18 16:41:03 CEST 2011
On Jul 18, 2011, at 10:11 AM, Ana Kolar wrote:
> Yes, indeed! I believe I should integrate differences of min of both
> functions, no? I'm not quite sure how this should be done in R
> therefore I was wondering if there are some build in functions that
> do this job already. If not I would appreciate any help of how
> should it be done otherwise.
?integrate # would seem to be the glaringly obvious help query
>
> Toy example of data is here:
>
> a <- matrix(runif(30))
> b <- matrix(runif(30))
That's not a well-defined example of functions even if we take the
index to be the x value. Presumably you have some sort of value in
mind for "a" at an x-value of 1.5 but it is not clear from what you
have presented.
?stepfun
?approxfun
A function takes inputs (on some continuous measurement scale) and
returns results. Perhaps you should be seeking some local mathematical/
statistical consulting resource.
--
David.
>
> I tried to calculate this overlap with "Istat" function but am not
> sure that it does the job right! This is the example:
>
> library(SDMTools)
> a <- matrix(runif(30))
> b <- matrix(runif(30))
> Istat(a,b)
>
> Many thanks for your response, David!
>
> Ana
>
>
>
> From: David Winsemius <dwinsemius at comcast.net>
> To: Ana Kolar <annakolar at yahoo.com>
> Cc: R <r-help at r-project.org>
> Sent: Monday, 18 July 2011, 15:45
> Subject: Re: [R] SDMTools package - calculating overlap?
>
>
> On Jul 18, 2011, at 9:40 AM, Ana Kolar wrote:
>
> > Dear R users,
> >
> > Any idea of how to calculate an area of an overlap between two
> functions? The only R build in function that I found is I Similarity
> Statistic for Quantifying Niche Overlap and I am really not sure if
> this function is producing exactly what I am interested in since I
> was plotting functions and often got confused results (for example:
> got high value for the overlap of one pair and low for the other
> pair, while from the plot it looked like the first pair was
> overlapping better.) Can anyone please explain what's the reason
> behind such a behaviour? And does anyone has a suggestion of what
> function could be used for a calculation of an overlap area? The
> problem with 'Istat' function is also that it requires both data
> sets to have the same length, while I would be more interested in a
> function that enables overlap calculation even if data sets have
> different length. Looking forward to hearing from you! Have a good
> day. Ana
>
> Shouldn't you be integrating their difference (or the absolute value
> of their differences depending on your definition of "overlap"). I
> fail in understanding your example. Where is/are the function(s)?
>
> >
> > library(SDMTools)
> > a <- matrix(runif(30))
> > b <- matrix(runif(30))
> > Istat(a,b)
> > [[alternative HTML version deleted]]
> --
> David Winsemius, MD
> West Hartford, CT
>
>
>
David Winsemius, MD
West Hartford, CT
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