replace values in spacetime (STFDF) object
What Martin wants, replacing a subset, is not possible for STFDF (or other ST*) objects, just as with Spatial* objects: library(sp) data(meuse) coordinates(meuse)=~x+y meuse[1, "zinc"] = 500 Error in meuse[1, "zinc"] = 500 : object of type 'S4' is not subsettable Indeed, as Aman suggests, this could be done by subsetting the data.frame slot, and meuse$zinc[1] = 500 is a nice/short form for meuse at data$zinc[1] = 500. the second form, meuse$zinc[1] = 500 really calls function "[<-.data.frame" whereas meuse[1,"zinc"]<-500 tries to call "[<-.SpatialPointsDataFrame", which is not available. The same is true for "[<-.STFDF". It would be helpful to get some more information why you would need to do such replacement. For the Spatial* classes this request is very rare, but in space-time everything might be different, and we'd like to hear the how/why. Best regards,
On 03/11/2011 09:54 PM, Aman Verma wrote:
Hi Martin, It would be very helpful if you provided a clear example of exactly what you wanted to extract from the object, but I'll make a guess. As the vignette (of the class STFDF) mentions, you can select a specific time range and spatial points very easily by the normal index mechanism: the first index is the time, and the second is the space. Continuing the example below, if you run stfdf It will give you three spatial points, four times, and 12 data points, one for each space time combination. Now, if you wanted to subset this object to select the just the first two points, and the first two times, then you could simply say: stfdf[1:2,1:2] And you'll see that there are exactly two points, two times, and four data points. Now, you might say, I don't want to select the "first" or the "second" time, but I want to select by a certain time itself, like after 11:30 on 2010-08-05. Take a look at the class of the stfdf at time object class(stfdf at time) You can see that it is a xts object. Check out the help file for this class: ?xts At the bottom, it gives you some great examples of how to subset these kind of time objects. So, now, you can try using these indices instead of the "number" of the time in your set. stfdf[,'2010-08-05 11:00:00::2010-08-05 12:00:00'] So that is how to select everything from 11:00 to 12:00 on that day. Now, you have to figure out how to subset the space object. You should be able to get the idea from above though: read the help files and google how to subset that specific object. You'll then be able to subset by index. Or, you could find all the points within a certain window (created by a SpatialPolygon) and then use the vector of logical as you index. aman -----Original Message----- From: Roth, M. [mailto:m.roth at tue.nl] Sent: March 11, 2011 3:17 PM To: Aman Verma; r-sig-geo at r-project.org Subject: RE: replace values in spacetime (STFDF) object Hi, thank you very much. But actually that is not exactly what I want to do. I want to select a specific time range and spatial points and manipulate the corresponding data. When I subset the dataframe I must do the selection manually and that is not that nice. Any idea how I could do this? Cheers, Martin
________________________________________
From: Aman Verma [aman.verma at mcgill.ca]
Sent: Friday, March 11, 2011 7:16 PM
To: Roth, M.; r-sig-geo at r-project.org
Subject: RE: replace values in spacetime (STFDF) object
Hi Martin,
You put the brackets in the wrong place. You want to subset the dataframe, right, not the stfdf object, so:
stfdf at data$values[1] <- stfdf at data$values[1] + 1
would increase the "value" in the first row of the stfdf at data data frame.
stfdf at data[,1]
would get you the first column of the data frame. If you wanted to increase the whole column by one:
stfdf at data[,1] = stfdf at data[,1] + 1
aman
-----Original Message-----
From: r-sig-geo-bounces at r-project.org [mailto:r-sig-geo-bounces at r-project.org] On Behalf Of Roth, M.
Sent: March 11, 2011 10:00 AM
To: r-sig-geo at r-project.org
Subject: [R-sig-Geo] replace values in spacetime (STFDF) object
Hello,
I want to replace specific values in a STFDF object from the spacetime package.
As example consider the following stfdf object out of the vignette.
sp = cbind(x = c(0,0,1), y = c(0,1,1))
row.names(sp) = paste("point", 1:nrow(sp), sep="")
sp = SpatialPoints(sp)
time = xts(1:4, as.POSIXct("2010-08-05", tz = "GMT")+3600*(10:13))
m = c(10,20,30) # means for each of the 3 point locations
mydata = rnorm(length(sp)*length(time),mean=rep(m, 4))
IDs = paste("ID",1:length(mydata), sep = "_")
mydata = data.frame(values = signif(mydata,3), ID=IDs)
stfdf = STFDF(sp, time, mydata)
Now I want to do something like this:
stfdf[ , 1]@data$values <- stfdf[ , 1]@data$values + 1
I get the following error:
Error in stfdf[, 1]@data$values <- stfdf[, 1]@data$values + 1 :
object of type 'S4' is not subsettable
Does anybody know how to do that in a correct way?
Thanks a lot,
Martin Roth
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