How to delete dupicates in array, but not just one element that have pair to make him unique, but both, or how much duplicates there is?

1

have: [ 1, 2, 3, 1, 2, 4, 5, 6, 2]
output: [ 3, 4, 5, 6]

I need this for: https://www.freecodecamp.com/challenges/symmetric-difference

2

Are you familar with the indexOf method of an array? You could use that to remove duplicates. You can loop through the array and then do a indexof of the item you are currently on. If you take your example of [ 1, 2, 3, 1, 2, 4, 5, 6, 2] the indexOf(1) is 0 since it is the first item in the array. As you loop through the array and you get to the second 1 which is in position 3 the indexOf(1) is 0 and 0 does not match the position 3 so that means it is a duplicate and you remove it.

Hope that helps.

1 Like
3

I think the easiest way to do this is with a map (or hash, or dictionary, depending on what your language calls it).

You’d have a map where the key is each integer, and the value is the count of instances of that integer in the array.

Example in Python:

#!/usr/bin/env python

from collections import defaultdict

input =  [1, 2, 3, 1, 2, 4, 5, 6, 2]

vals = defaultdict(lambda: 0)

for val in input:
    vals[val] += 1

output = [key for key, val in vals.items() if val == 1]

print output

Output:

[3, 4, 5, 6]

Example in Go:

package main

import (
    "fmt"
)

func main() {
    input := []int{1, 2, 3, 1, 2, 4, 5, 6, 2}
    vals := make(map[int]int)
    for _, val := range input {
        vals[val]++
    }
    output := make([]int, 0)
    for key, val := range vals {
        if val == 1 {
            output = append(output, key)
        }
    }
    fmt.Println(output)
}

Output:

[3 4 5 6]
4

In JS, can something like this:

function filterer(array){
  
   var have = {};
   return array.filter(function(val) {
     return have.hasOwnProperty(val) ? false : (have[val] = true);
      });


}