[R] How to average values from grid cells with coordinates

[Jim Lemon]

Hi lili,
You can extend it like this. I checked this with two values each for
pop and mood, and it looked okay. Obviously I didn't check the result
with 365 values for each, but it ran okay.

# these values are the centers of the black cells
lat<-rep(28:38,11)
lon<-rep(98:108,each=11)
pop<-matrix(sample(80:200,44165,replace=TRUE),ncol=365)
colnames(pop)<-paste0("pop",1:365)
mood<-matrix(sample(1:10,44165,replace=TRUE),ncol=365)
colnames(mood)<-c("mood",1:365)
# create the data frame for the black cells
blackcells<-cbind(data.frame(lat=lat,lon=lon),pop,mood)
plot(0,type="n",xlim=c(97.5,108.5),ylim=c(27.5,38.5),
 xlab="Longitude",ylab="Latitude")
abline(h=27.5)
abline(h=lat+0.5)
abline(v=97.5)
abline(v=lon+0.5)
# the red cells will be centered on the corners of 4 black cells
lat2<-rep(seq(28.5,34.5,by=2),4)
lon2<-rep(seq(99.5,105.5,by=2),each=4)
popmat<-matrix(NA,nrow=16,ncol=365)
colnames(popmat)<-paste0("pop",1:365)
moodmat<-matrix(NA,nrow=16,ncol=365)
colnames(moodmat)<-paste0("mood",1:365)
redcells<-cbind(data.frame(lat=lat2,lon=lon2),popmat,moodmat)
#display the red cells
rect(lon2-1,lat2-1,lon2+1,lat2+1,border="red",lwd=2)
nblackcells<-dim(blackcells)[1]
nredcells<-dim(redcells)[1]
for(redcell in 1:nredcells) {
 close4<-rep(NA,4)
 closen<-1
 for(blackcell in 1:nblackcells) {
  if(abs(blackcells[blackcell,"lat"]-redcells[redcell,"lat"]) < 1 &&
   abs(blackcells[blackcell,"lon"]-redcells[redcell,"lon"]) < 1) {
   close4[closen]<-blackcell
   closen<-closen + 1
  }
 }
 redcells[redcell,3:730]<-colMeans(blackcells[close4,3:730])
}

Jim

On Tue, May 22, 2018 at 1:37 PM, lily li <chocold12 at gmail.com> wrote:
> Hi Jim,
>
> Thanks. It works. I now have more complex problems. If at each blackcell,
> there are two variables such as pop and mood. For each variable, there are
> daily records in one year, so 365 records for pop and 365 records for mood.
> The averaged values for the redcells should be daily records too. What kind
> of format do you recommend for this problem? Right now, I just get the
> latitudes and longitudes into a dataframe. Thanks.
>