R: replacing NA with value of closest point

Question

Here is an example of a problem I am attempting to solve and implements in a much larger database: I have a sparse grid of points across the new world, with lat and long defined as below. ``` LAT<-rep(-5:5*10, 5) LON<-rep(seq(-140, -60, by=20), each=11) ``` I know the color of some points on my grid ``` COLOR<-(c(NA,NA,NA,"black",NA,NA,NA,NA,NA,"red",NA,NA,"green",NA,"blue","blue",NA,"blue",NA,NA,"yellow",NA,NA,"yellow",NA+ NA,NA,NA,"blue",NA,NA,NA,NA,NA,NA,NA,"black",NA,"blue","blue",NA,"blue",NA,NA,"yellow",NA,NA,NA,NA,"red",NA,NA,"green",NA,"blue","blue")) data<-as.data.frame(cbind(LAT,LON,COLOR)) ``` What I want to do is replace the NA values in COLOR with the color that is closeset (in distance) to that point. In the actual implementation, I am not worried too much with ties, but I suppose it is possible (I could probably fix those by hand). Thanks

Accepted Answer

Yup.

First, make your data frame with `data.frame` or things all get coerced to characters:

```
data<-data.frame(LAT=LAT,LON=LON,COLOR=COLOR)
```

Split the data frame up - you could probably do this in one go but this makes things a bit more obvious:

```
query = data[is.na(data$COLOR),]
colours = data[!is.na(data$COLOR),]
library(FNN)
neighs = get.knnx(colours[,c("LAT","LON")],query[,c("LAT","LON")],k=1)
```

Now insert the replacement colours directly into the `data` dataframe:

```
data[is.na(data$COLOR),"COLOR"]=colours$COLOR[neighs$nn.index]
plot(data$LON,data$LAT,col=data$COLOR,pch=19)
```

Note however that distance is being computed using pythagoras geometry on lat-long, which isn't true because the earth isn't flat. You might have to transform your coordinates to something else first.

R: replacing NA with value of closest point

Solution

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