CODEWITHSUNDEEP
javascriptmultidimensional-array
pooh
pooh

Reputation: 33

Insert value into a Javascript array randomly

I created a table using an 8x8 matrix for a game and i also put into the table prizes, and etc in random places but I am having an issue creating also random start position for the user that doesn't conflict with the objects that are already in the table.

For now I have:

function startPos(matrix) {
  var x = Math.round(Math.random() * matrix.length);
  var y = Math.round(Math.random() * matrix.length);

  while (matrix[y][x] != undefined) {
    var x = Math.round(Math.random() * matrix.length);
    var y = Math.round(Math.random() * matrix.length);
    return matrix[y][x];
  };


  return matrix[y][x];
};

but I get nothing. Sorry if the question seems trivial I am just starting Javascript and have looked everywhere for a relevant answer with no avail.

Upvotes: 3

Views: 1941

Answers (2)

Nathan Jones
Nathan Jones

Reputation: 28

It looks like what you want to do is select a random position in the matrix, if it is undefined then return it, otherwise select a new random position and try again. You need to make a few changes for this.

First - the return statement in your loop is unnecessary and is causing your function to be returned on the first run of the loop, stopping it from doing its job.

Second - In most cases, you should use === and !== instead of == and !=. You can find a detailed explanation here - Which equals operator (== vs ===) should be used in JavaScript comparisons?

Third - When you want to check if a variable is undefined, while myVar === undefined should work most of the time, there a situations where it could fail. best practice is to use typeof myVar === 'undefined'. More info here - https://stackoverflow.com/a/15093969/7739148

try this:

function startPos(matrix){
  // first select a random position
  var x = Math.round(Math.random() * matrix.length);
  var y = Math.round(Math.random() * matrix.length);

  // if the position is not empty, select a new one.
  // continue like this until an empty spot is found.
  while(typeof matrix[y][x] !== 'undefined'){
    x = Math.round(Math.random() * matrix.length);
    y = Math.round(Math.random() * matrix.length);
  };

  // once we have an empty position, return it
  return matrix[y][x];
};

Caution - if there are no positions that are undefined the loop will never end, so you should either make sure your matrix will have at least one empty spot, or perform a check at the start of your function.

Upvotes: 0

Bergi
Bergi

Reputation: 664356

A few mistakes:

  • you must not return from within the loop, but have to check the condition to leave it
  • you need to use Math.floor instead of Math.round
  • you need to return the position, not the value of the field (which you just asserted to be undefined)

function startPos(matrix) {
  var l = matrix.length; // assumes square matrix
  do { // assumes at least one empty field
    var x = Math.floor(Math.random() * l);
    var y = Math.floor(Math.random() * l);
  } while (matrix[y][x] != undefined);
  return [y, x];
}

Upvotes: 1

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