ranger out-of-bag proximity matrix

I’ve created a function to compute an out-of-bag proximity matrix of a ranger object, based on edarf::extract_proximity:

extract_proximity_oob = function(fit, olddata) {
  pred = predict(fit, olddata, type = "terminalNodes")$predictions
  prox = matrix(NA, nrow(pred), nrow(pred))
  ntree = ncol(pred)
  n = nrow(prox)
  
  if (is.null(fit$inbag.counts)) {
    stop("call ranger with keep.inbag = TRUE")
  }
  
  # Get inbag counts
  inbag = simplify2array(fit$inbag.counts)
  
  for (i in 1:n) {
    for (j in 1:n) {
      # Use only trees where both obs are OOB
      tree_idx = inbag[i, ] == 0 & inbag[j, ] == 0
      prox[i, j] = sum(pred[i, tree_idx] == pred[j, tree_idx]) / sum(tree_idx)
    }
  }
  
  prox
}

(taken from https://github.com/imbs-hl/ranger/issues/234)