R code for selecting places spatially and by time
Andrew, You haven't defined the problem clearly, but I will try to guess what you mean...
i.e. what properties are within 3 km from properties infected on "2008-01-01" over the last 14 days.
I'm guessing that each row of your sample data represents one
infection event, and you want to find all rows where the date is
within 14 days following "2008-01-01" and the location is within 3 km
of any of the sites listed as "2008-01-01".
Presumably the x and y coordinates are already in units of metres;
otherwise use "project" in package rgdal.
Then:
x <- rep(c(2660156,2660203,2658165,2659303,2661531,2660914),c(2,2,2,2,1,1)
)
y <- rep(c(6476767,6475013,6475487,6479659,6477004,6476388),c(2,2,2,2,1,1)
)
date <- rep(as.Date(c("2008-01-02","2008-01-17","2008-01-01"),
format = "%Y-%m-%d"),c(4,4,2))
## the set of properties or infections or something
props <- data.frame(x, y, date)
## find indices of source events
src.date <- as.Date("2008-01-01")
src.i <- which(date == src.date)
## distances between properties
dists <- as.matrix(dist(cbind(x,y)))
## select sites within space and time bounds
hits <- FALSE
for (i in src.i) {
i.hits <- (src.date < date) & (date <= src.date + 14) &
(dists[i,] < 3000)
hits <- hits | i.hits
}
## look at matching sites
props[hits,]
## look at distances of matching sites from source sites
dists[src.i,hits]
It would also be possible to do it more efficiently if that is an issue.
On Fri, Mar 7, 2008 at 9:40 AM, Andrew McFadden
<Andrew.McFadden at maf.govt.nz> wrote:
Hi all
The code of trying to write relates to selecting properties (given by x
and y co-ordinates) spatially (distance "X" from "infected" properties
identified by date) over a certain time period.
i.e. what properties are within 3 km from properties infected on
"2008-01-01" over the last 14 days.
Is any one able to give me some clues on how to write code to solve this
problem.
Some sample data is as follows:
x<-rep(c(2660156,2660203,2658165,2659303,2661531,2660914),c(2,2,2,2,1,1)
)
y<-rep(c(6476767,6475013,6475487,6479659,6477004,6476388),c(2,2,2,2,1,1)
)
date<-as.character(rep(as.Date(c("2008-01-02","2008-01-17","2008-01-01")
,format = "%Y-%m-%d"),c(4,4,2)))
cbind(x,y,date)
Regards
Andrew
Andrew McFadden MVS BVSc
Incursion Investigator
Investigation & Diagnostic Centres - Wallaceville Biosecurity New
Zealand Ministry of Agriculture and Forestry
Phone 04 894 5600 Fax 04 894 4973 Mobile 029 894 5611 Postal address:
Investigation and Diagnostic Centre- Wallaceville Box 40742 Ward St
Upper Hutt
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