Find duplicate values in objects with Javascript

Question

I\'ve been trying to work out a problem I\'m having. I have an array with objects in it, like this:

var array = [
  {
    name: \"Steven Smith\",
    Country         


        

Answer 1

Here's an alternative solution, which I will point out the

let array      = getData();                       // sets up data array
let duplicates = array.filter(duplicatesOnly);    // filter out duplicates

console.log( duplicates );                        // output to console



/* ============================================================================= */


// Returns true/false based on a duplicate object being found   
function duplicatesOnly(v1, i1, self) {
  let ndx = self.findIndex(function(v2, i2) {
    // make sure not looking at the same object (using index to verify)
    // use JSON.stringify for object comparison
    return (i1 != i2 && JSON.stringify(v1) == JSON.stringify(v2))
  })
  return i1 != ndx && ndx != -1
}


// Use function hoisting to place trivial code at the bottom of example
function getData() {
  return [{
      name: "Steven Smith",
      Country: "England",
      Age: 35
    },
    {
      name: "Hannah Reed",
      Country: "Scottland",
      Age: 23
    },
    {
      name: "Steven Smith",
      Country: "England",
      Age: 35
    },
    {
      name: "Robert Landley",
      Country: "England",
      Age: 84
    },
    {
      name: "Steven Smith",
      Country: "England",
      Age: 35
    },
    {
      name: "Robert Landley",
      Country: "England",
      Age: 84
    }
  ];
}

Benefits

• Heart of code is 3 lines
• Code is clear
• Easy to maintain

Costs

• Performance
  • JSON.stringify is being performed on two objects on each iteration (very expensive)
  • Complexity: O(N^2) -- the bigger the array, the slower it may become

Notes

---

• JSON.stringify may create the string based on key order, so even if objects have the same keys/values, the order may be a factor when comparing the objects -- this could be seen as a benefit or a cost
• This is an example of using filter and findIndex the concentration was not on making it efficient. It could be improved by using caching and performing JSON.stringify once, or avoiding it altogether with something more customized.