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

[Rafael Wüest]

Hi Tiffany,

If I got your initial question right, you want to apply the MannKendall test to the whole raster. If so, you may use the calc() command.

Something like

myraster.mk <- calc(myraster,function(x){MannKendall(rev(x))$sl})

may give you what you need.

HTH, Rafi

On 03.08.2012, at 03:37, Thiago Veloso wrote:

>   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
> 
> 
>     [[alternative HTML version deleted]]
> 
> 
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> 
> 
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo



--
Rafael Wüest
Swiss Federal Research Institute WSL
Zürcherstrasse 111
8903 Birmensdorf
Switzerland

+41 44 7392126
rafael.wueest at wsl.ch
http://www.wsl.ch/info/mitarbeitende/wueest/index_EN