[R] matrix help (first occurrence of variable in column)

[jim holtman]

Is this what you were after:

> mdat <- matrix(c(1,0,1,1,1,0), nrow = 2, ncol=3, byrow=TRUE,
+               dimnames = list(c("T1", "T2"),
+                               c("sp.1", "sp.2", "sp.3")))
>
> mdat
   sp.1 sp.2 sp.3
T1    1    0    1
T2    1    1    0
> # do 'rle' on each column and see if it is length >1 and starts with zero
> mdat.df <- as.data.frame(mdat)
> new.spec <- sapply(mdat.df, function(x){
+     x.rle <- rle(x)
+     (length(x.rle$values) > 1) & (x.rle$values[1L] == 0)
+ })
> names(mdat.df)[new.spec]
[1] "sp.2"
>


On Wed, May 18, 2011 at 9:37 AM, Michael Denslow
<michael.denslow at gmail.com> wrote:
> Dear R help,
> Apologies for the less than informative subject line. I will do my
> best to describe my problem.
>
> Consider the following matrix:
>
> mdat <- matrix(c(1,0,1,1,1,0), nrow = 2, ncol=3, byrow=TRUE,
>               dimnames = list(c("T1", "T2"),
>                               c("sp.1", "sp.2", "sp.3")))
>
> mdat
>
> In my actual data I have time (rows) and species occurrences (0/1
> values, columns). I want to count the number of new species that occur
> at a given time sample. For the matrix above the answer would be 1.
>
> Is there a simple way to figure out if the species has never occurred
> before and then sum them up?
>
> Thanks in advance,
> Micheal
>
> --
> Michael Denslow
>
> I.W. Carpenter Jr. Herbarium [BOON]
> Department of Biology
> Appalachian State University
> Boone, North Carolina U.S.A.
> -- AND --
> Communications Manager
> Southeast Regional Network of Expertise and Collections
> sernec.org
>
> 36.214177, -81.681480 +/- 3103 meters
>
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>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?