[R-sig-Geo] Mann-Kendall test on raster data

[Thiago Veloso]

  Tiffany,

  You can use raster's "rasterfromXYZ" function.

  And it's not necessary to write out and read in the file, unless it's convenient to you.

  Hph,
  Thiago.


----- Original Message -----
From: Tiffany Smith <smithtiffanyt at gmail.com>
To: r-sig-geo at r-project.org
Cc: 
Sent: Thursday, August 2, 2012 3:26 PM
Subject: Re: [R-sig-Geo] Mann-Kendall test on raster data

An update, I have been able to automate the MannKendall test and capture the output into a .txt file:

lat<-seq(-125,-67,0.5)
lon<-seq(25,53,0.5)

fun.mk<-function(x){
    for (i in 1:length(lat)){
        for (j in 1:length(lon)){
            v<-rev(extract(x,SpatialPoints(cbind(lat[i],lon[j]))))
            mk<-MannKendall(v)
            pv<-mk$sl
            out<-data.frame(cbind(lat[i],lon[j],pv[1]))
            write.table(out,"myraster.mk.txt",append=TRUE,col.names=FALSE,row.names=FALSE,quote=FALSE)
            }}}
myraster.mk<-fun.mk(myraster)

Now, I would like to read that file back into R as a RasterLayer. So far, I can read it in as a table to get:

myraster.table<-read.table("myraster.mk.txt",header=FALSE) 
myraster.table
        V1     V2          V3
1  -86.000 35.000 0.071539655
2  -86.000 35.125 0.004216323
3  -86.000 35.250 0.449751556
4  -86.000 35.375 0.124644011
5  -86.000 35.500 0.128179774
…

In the Raster package, there is "as.data.frame" to go from raster->data.frame but I can't find anything to go in the opposite direction, data.frame->raster. I tried using "as.raster", but that didn't work:

myraster.raster<-as.raster(myraster.table)
Error in UseMethod("as.raster") : 
  no applicable method for 'as.raster' applied to an object of class "data.frame"

Thanks,
Tiffany
On Aug 1, 2012, at 6:24 PM, Tiffany Smith wrote:

> Hello,
> 
> I'm trying to do a Mann-Kendall test on my RasterBrick data. So far, I've been able to complete the Mann-Kendall test (via the "Kendall" package) by extracting a series like so:
> 
> onelocation<-rev(extract(myraster,SpatialPoints(cbind(-86,33))))
> onelocation.mk<-MannKendall(onelocation)
> 
> I need help either figuring out a way to do the MK test with raster data, or if I loop through all points and use the above commands, how can I return that data into a Raster so I can visualize the results by making maps?
> 
> Thanks,
> Tiffany


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