How to average values from grid cells with coordinates

Hi lily,
There are one or two assumptions to be made here. First is that the
latitude and longitude values of the "black" cells are equally spaced
as in your illustration. Second, that all latitude and longitude
values for the "red" cells fall at the corners of four "black" cells.

You can get the four "black" cells by finding the lat/lon values that
are closest to the "red" lat/lon values. Here's a basic example:

lat<-rep(28:38,11)
lon<-rep(98:108,each=11)
pop<-sample(80:200,121)
blackcells<-list()
for(i in 1:121) blackcells[[i]]<-list(lat=lat[i],lon=lon[i],pop=pop[i])
redcell<-list(lat=33.5,lon=100.5,pop=NA)
close4<-rep(NA,4)
closen<-1
for(i in 1:121) {
 if(abs(blackcells[[i]]$lat-redcell$lat) < 1 &&
  abs(blackcells[[i]]$lon-redcell$lon) < 1) {
  close4[closen]<-i
  closen<-closen+1
 }
}
cat(close4,"\n")
redcell$pop<-(blackcells[[close4[1]]]$pop +
 blackcells[[close4[2]]]$pop + blackcells[[close4[3]]]$pop +
 blackcells[[close4[4]]]$pop)/4
print(blackcells[[close4[1]]])
print(blackcells[[close4[2]]])
print(blackcells[[close4[3]]])
print(blackcells[[close4[4]]])
print(redcell)

As you can see, this has picked out the four "black" cells closest to
the "red" cell's coordinates and calculated the mean.

Jim

On Wed, May 16, 2018 at 2:23 PM, lily li <chocold12 at gmail.com> wrote:

Hi R users,

I have a question about data processing. I have such a dataset, while

each

black grid cell has a few attributes and the corresponding attribute
values. The latitude and longitude of the center of each grid cell are
given also.

Then I want to average the attribute values from four adjacent grid cells
to get the average value for the center of each red grid cell. Thus,

there

are the same number of attributes, but different values. The red grid

cells

do not overlap. I was thinking to write such a script that can ID each
black grid cell, for example, 1, 2, 3, 4, ..., then the corresponding

four

grid cells will be used to average for the red grid cell. But I just have
the latitude and longitude, attribute values for the black cells, and

also

latitude and longitude for the red cells, how to write such a script in

R.

Could anyone give me suggestion about the work flow? Thanks very much.

I attached the picture of the grid cells here.

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