Merge data.table by two nearest variables

Question

I have two data tables with x,y coordinates and some other info which I would like to merge based on nearest neighbour distance, i.e. on the minimum in squared difference of

Answer 1

One possible solution:

func = function(u,v)
{
    vec = with(DT2, (u-x)^2 + (v-y)^2)
    DT2[which.min(vec),]$Q
}

transform(DT1, Q=apply(DT1, 1, function(u) func(u[1], u[2])))

#   x y Q
#1: 1 3 a
#2: 2 4 d
#3: 3 5 d
#4: 4 6 e
#5: 5 7 e