CODEWITHSUNDEEP
r
DJ-AFC
DJ-AFC

Reputation: 569

Find closest set of coordinates between two matrices

I have two matrices as follows:

OBS = matrix(data=c(0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 
0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 
3, 4, 2, 4, 3, 5), 
nrow=6, ncol=3)
colnames(OBS)=c("Lat", "Lon", "Tas")

OBS = data.frame(OBS)

MOD = matrix(data=c(1.5, 3.0, 0.0, 0.0, 3, 4), nrow=2, ncol=3)
colnames(MOD)=c("Lat", "Lon", "Tas")

MOD = data.frame(MOD)

I want to use the coordinates in OBS and search for the closest set of coordinates from MOD and return the corresponding Tas values. The output should therefore be:

OUT = data.frame(c(3, 3, 3, 3, 4, 4))

I have applied the following solution:

library(geosphere)

# create distance matrix
mat <- distm(OBS[,c('Lon','Lat')], MOD[,c('Lon','Lat')], 
fun = distVincentyEllipsoid)

# Find shortest distance in matrix and assign tas values from MOD
OUT <- MOD$Tas[max.col(-mat)]

This works fine for this example, but if you try with datasets with several hundred or more rows then it no longer works. Anyone know why?

Upvotes: 0

Views: 78

Answers (1)

ThomasIsCoding
ThomasIsCoding

Reputation: 102920

Maybe you can try the following code to see if it can work with larger dataset

OUT <- data.frame(x = MOD$Tas[apply(abs(outer(OBS$Lat+1i*OBS$Lon,MOD$Lat+1i*MOD$Lon,"-")),1,which.min)])

such that

> OUT
  x
1 3
2 3
3 3
4 3
5 4
6 4

Upvotes: 1

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