How to remove all element after a specific element of array?

Question

Below is my array....

["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD"]

What can I do to get a array back like ["AAA", "BBB", "CCC"]

for example, if the first element is "AAA", I want to delete all element after second "AAA"(second "AAA" also remove)

Thanks.

Answer 1

You can do this easily using indexOf and slice methods of array in javascript.

var arr = ["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD"];
var firstElem = arr[0];
var secondIndex = arr.indexOf(firstElem, 1);

// Output: ["AAA", "BBB", "CCC"]
var newArr = (secondIndex != -1) ? arr.slice(0, secondIndex) : arr;

Working Fiddle: https://jsfiddle.net/4f25wyaj/2/

Answer 2

You can use Array.prototype.filter(), reference first element of array to check if the value has been iterated

var arr = ["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD"]

var again = false;

arr = arr.filter(function(el, index) {
  return !again && (again = index > 0 && el === arr[0], !again);
});

console.log(arr);

Answer 3

Faster implementation (Better for short or medium size arrays):

var a = ["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD"];

// Faster implementation:
// (Better for short or medium size arrays)
var b = a.filter((function(){
    var idx = {};
    var cont = true; // Continue
    return function (item){
        if (! cont) return false;
        if (idx[item]) return cont = false;
        return idx[item] = true;
    };
})());

console.log(b);
// [ 'AAA', 'BBB', 'CCC' ]

Implementation with minimal memory waste (but highly unefficient):

// Minimal memory waste implementation:
var b = a.filter((function(){
    var cont = true; // Continue
    return function (item, i){
        if (! cont) return false;
        if (a.slice(0, i).filter(x=>x==item).length) return cont = false;
        return true;
    };  
})());

console.log(b);
// [ 'AAA', 'BBB', 'CCC' ]

Of course, there is infinite intermediate approaches (depending on your needings). But, If you donsn't need to parse HUGE arrays, the best solution is to use the first approach: Index will be freed by garbage collector as soon as filter process finishes and, in fact, if you are lucky and repetition happen early, then no much memory will be used ;-)

Answer 4

Quick and dirty using jQuery each() function.

each() goes through the array and adds elements to new array until a duplicate of the first element is found.

var arr = ["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD"];
var newArray = [];
$.each(arr, function(i, el){
    if($.inArray(el, newArray) === -1) 
      newArray.push(el);
    else if (el == arr[0])
      return false
});
arr = newArray;
// Formatted array is in "arr"
alert(arr);

Answer 5

Though Your question is not fully clear but still as per my understanding I am providing following solutions

Solution 1:
 Assumption: You have a list of input and a pointer which shows the last index till you want to pick the input data.

    public static void main(String[] args) {
        String input[] = { "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD" };
        String output[]= new String[5];
        int stopByIndex =3;

        for(int i=0;i<stopByIndex;i++){
            output[i]=input[i];
        }
        System.out.println(output);
    }


 Solution 2:
Assumption: Print elements which occurred multiple times:

  public static void main(String[] args) {
    String input[] = { "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "DDD" };
    List<String> output = new ArrayList<>();
    Map<String, Integer> keyWithCount = new HashMap<String, Integer>();
    int stopByIndex = 3;

    for (String str : input) {
        if (keyWithCount.containsKey(str)) {
            keyWithCount.put(str, keyWithCount.get(str) + 1);
        } else {
            keyWithCount.put(str, 1);
        }
    }

    Iterator<Entry<String, Integer>> itr = keyWithCount.entrySet().iterator();
    while (itr.hasNext()) {
        Entry<String, Integer> entry = itr.next();

        if (entry.getValue() > 1) {
            output.add(entry.getKey());
        }
    }

    System.out.println(output);
}

Answer 6

Try this:

var arr = ["AAA", "BBB", "CCC", "AAA", "BBB", "CCC", "AAA", "BBB", "CCC",     "DDD"];

arr.splice(3)