What the best way to find minimal difference and corresponding value with element-wise vector comparison?

Question

I have one problem.
Vector A is the query, Vector B is the ref.
I want to see which value of A is the closest to one of the B value.
Both vectors are ordered.

INPUT

A = c(1, 1.2, 4, 8, 9, 10, 30)
B = c(0.1, 3.9)

OUTPUT

min_diff_value = 0.1
min_value_A = 4
min_value_B = 3.9 (optionnal)

I want to know if there may be a trick to perform this without time-consuming loop?
Thank you.

Answer 1

You could use outer

A = c(1, 1.2, 4, 8, 9, 10, 30)
B = c(0.1, 3.9)

mat <- outer(A, B, `-`)
min_diff_value <- min(abs(mat))
dim <- which(mat == min_diff_value, arr.ind = TRUE)
min_value_A <- A[dim[, 1]]
min_value_B <- B[dim[, 2]]

min_diff_value
#[1] 0.1
min_value_A
#[1] 4
min_value_B
#[1] 3.9