Unintended duplicate output in series of objects

Question

I am having an issue with the following code. It is designed to remove duplicates (third and final entries) from an array of objects formatted as

{x: val, y: val2}

However, I will occasionally get outputs with duplicates (image) such as:

Object {x: 5, y: 0}
Object {x: 7, y: 0}
Object {x: 7, y: 5}
Object {x: 5, y: 2}
Object {x: 2, y: 1}
Object {x: 7, y: 5}

Why is this code not removing the duplicates as it is supposed to?

var mines = [{}];
console.log("\n\n\n\n\n");
for (var i = 0; i < 10; i++){ //for each mine that needs to be made
  var mine = {}; //initalize temporary object
  var dupeerr = false; //set duplication error flag to false 
                       //(will be flipped if loop needs to be re-executed)
  do{
    //generate coordinates for new mine
    //(random int between 0 and max size), then rounded to
    mine.x = Math.round(Math.random()*(8));
    mine.y = Math.round(Math.random()*(9));
    for (var j = mines.length - 1; j >= 0; j--) { //for each mine in array
      if ((mines[j].x == mine.x) && (mines[j].y == mine.y)) { //check for doubles
        dupeerr = true; //flag for re-execution
      } else if (mines[j] != mine) {
        dupeerr = false;
      }
    };
    //console.log(mines);
  } while (dupeerr || bounderr);

  mines[i] = mine;
}
var ans = [];

for (var i = 0; i < mines.length; i++) {
  ans[i] = mines[i];
  var minebtn = document.getElementById(JSON.stringify(ans[i]));
  console.log(ans[i]);
};

is you question "why is this code not removing duplicates", or "how do I do what I want to do?" because if it's the latter, there's a nicely creative answer. — Mike 'Pomax' Kamermans
– Mike 'Pomax' Kamermans, Commented Jun 19, 2013 at 1:47

asafreedman · Accepted Answer · 2013-06-19 01:47:18Z

4

The problem is your for loop:

for (var j = mines.length - 1; j >= 0; j--) { //for each mine in array
  if ((mines[j].x == mine.x) && (mines[j].y == mine.y)) { // check for doubles
    dupeerr = true; //flag for re-execution
    break; // This should be sufficient to break you out of the for loop on true
  } else if (mines[j] != mine) {
    dupeerr = false;
  }
};

Even if it finds one it will continue on. On the next try it may be false and overwrite dupeerr to false.

answered Jun 19, 2013 at 1:47

asafreedman

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1 Comment

asafreedman Over a year ago

OP never resets the dupeerr flag in the 'do' loop on exit of the 'for' loop. So, you'd be right if the logic was shifted around a little. The comparison in the 'else if' block may be unnecessary.

elclanrs · Accepted Answer · 2013-06-19 01:52:11Z

1

You could do this with JSON. It's kind of hacky but it should work fine for simple objects:

var arr = [{x:1,y:1}, {x:1,y:2}, {x:1,y:1}, {x:1,y:2}];

function removeDups(arr) {
  return arr
    .map(JSON.stringify)
    .filter(function(v,i,self){ return self.indexOf(v) == i })
    .map(JSON.parse);
}

console.log(removeDups(arr)); //=> [{x:1,y:1}, {x:1,y:2}]

edited Jun 19, 2013 at 1:52

answered Jun 19, 2013 at 1:43

elclanrs

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3 Comments

user2437417 Over a year ago

When a duplicate object is generated, it should be flagged in the inner loop, keeping it running until a unique one is made. Trouble is that OP is resetting the flag to false on the next iteration when a dupe is found.

user2437417 Over a year ago

...and FWIW, you can do .map(JSON.stringify) and .map(JSON.parse).

elclanrs Over a year ago

@CrazyTrain: Of course, silly me. Well I'll leave the question here if this helps OP even tho it doesn't really solve the problem.

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