[R-sig-Geo] replace values in spacetime (STFDF) object

[Aman Verma]

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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