[R] How to create gridded data

[Jim Lemon]

Hi lily,
Something like this should work:

DF1<-read.table(text=
"latitude   longitude   Precip
45.5           110.5         3.2
45.5           111            5.0
45.5           111.5         1.8
45.5           112            2.0
46              110.5         6.1
46              111            4.5
46              111.5         7.8
46              112            5.5",
header=TRUE)
lats<-sort(unique(DF1$latitude),decreasing=TRUE)
lons<-sort(unique(DF1$longitude))
DF2<-matrix(NA,nrow=length(lats),ncol=length(lons))
rownames(DF2)<-lats
colnames(DF2)<-lons
nval<-dim(DF1)[1]
for(val in 1:nval) {
 row<-which(lats == DF1$latitude[val])
 col<-which(lons == DF1$longitude[val])
 DF2[row,col]<-DF1$Precip[val]
}

Jim

On Tue, Nov 13, 2018 at 6:22 PM lily li <chocold12 using gmail.com> wrote:
>
> Hi R users,
>
> I have a question about manipulating data. For example, I have DF1 as the
> following, how to transform it to a gridded dataset DF2? In DF2, each value
> Precip is an attribute of the corresponding grid cell. So DF2 is like a
> spatial surface, and can be imported to ArcGIS. Thanks for your help.
>
> DF1
> latitude   longitude   Precip
> 45.5           110.5         3.2
> 45.5           111            5.0
> 45.5           111.5         1.8
> 45.5           112            2.0
> 46              110.5         6.1
> 46              111            4.5
> 46              111.5         7.8
> 46              112            5.5
> ...
>
>
> DF2
> 6.1   4.5   7.8   5.5
> 3.2   5.0   1.8   2.0
> ...
>
>         [[alternative HTML version deleted]]
>
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