Two methods for generating a random distance matrix one in Elm and one in Javascript.

Distances.elm

import Array
import Debug
import Random
import Matrix

planetNames : Array.Array String
planetNames = Array.fromList [
  "Terra",
  "Vulcan",
  "Omicron Persei 8",
  "Altair III",
  "Qo'noS" ]

planetDistances : Random.Seed -> Matrix.Matrix Int
planetDistances seed =
  let
    numPlanets = Array.length planetNames
    --Get a whole bunch of random distances (one for each pair of planets i.e n^2)
    (randomDistances, seed') = Random.generate (Random.list (numPlanets * numPlanets) (Random.int 1 10000)) seed
    randomMatrix = Array.indexedMap
      (\index planet ->
        let
          --Get a subset of the random numbers that we generated earlier
          randomSubset = List.take numPlanets (List.drop (index * numPlanets) randomDistances)
        in
          Array.fromList randomSubset) planetNames
    mirroredMatrix = mirrorMatrix randomMatrix
    finalMatrix = zeroDiagonal mirroredMatrix
    foo = Debug.log "Distances" finalMatrix
  in
    finalMatrix

--copies the bottom left of the matrix over to the top right
mirrorMatrix : Matrix.Matrix Int -> Matrix.Matrix Int
mirrorMatrix matrix =
  Matrix.mapWithLocation
    (\(x, y) distance ->
      if x < y then
        distance
      else
        Maybe.withDefault 0 (Matrix.get (y, x) matrix))
    matrix

zeroDiagonal : Matrix.Matrix Int -> Matrix.Matrix Int
zeroDiagonal matrix =
  Matrix.mapWithLocation (\(x, y) distance -> if x == y then 0 else distance) matrix

distances.js

var planets = [
  "Terra",
  "Vulcan",
  "Omicron Persei 8",
  "Altair III",
  "Qo'noS" ]

function planetDistances() {
  var numPlanets = planets.length;
  var distances = [];
  //Initialise the matrix (this wouldn't be necessary in Java)
  for (var i = 0; i < numPlanets; i++) {
    distances[i] = []
    distances[i][i] = 0
  }
  for (var i = 0; i < numPlanets; i++) {
    for (var j = 0; j < i; j++) {
      var randomValue = Math.floor(Math.random() * 10000)
      distances[i][j] = randomValue
      distances[j][i] = randomValue
    }
  }
  return distances
}