Calculating all distances between one point and a group of points efficiently in R

Question

First of all, I am new to R (I started yesterday).

I have two groups of points, data and centers, the first one of size n and

Answer 1

Rather than iterating across data points, you can just condense that to a matrix operation, meaning you only have to iterate across K.

# Generate some fake data.
n <- 3823
K <- 10
d <- 64
x <- matrix(rnorm(n * d), ncol = n)
centers <- matrix(rnorm(K * d), ncol = K)

system.time(
  dists <- apply(centers, 2, function(center) {
    colSums((x - center)^2)
})
)

Runs in:

utilisateur     système      écoulé 
      0.100       0.008       0.108 

on my laptop.