# How to remove repeated entries from an array while preserving non-consecutive duplicates?

I have an array like var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5]; I really want the output to be [5,2,9,4,5]. My logic for this was:

• Go through all the element one by one.
• If the element is the same as the prev element, count the element and do something like newA = arr.slice(i, count)
• New array should be filled with just identical elements.
• For my example input, the first 3 elements are identical so newA will be like arr.slice(0, 3) and newB will be arr.slice(3,5) and so on.

I tried to turn this into the following code:

function identical(array){
var count = 0;
for(var i = 0; i < array.length -1; i++){
if(array[i] == array[i + 1]){
count++;
// temp = array.slice(i)
}else{
count == 0;
}
}
console.log(count);
}
identical(arr);

I am having problems figuring out how to output an element that represents a group of element that are identical in an array. If the element isn't identical it should be outputted in the order that it is in in the original array.

Using array.filter() you can check if each element is the same as the one before it.

Something like this:

var a = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5];

var b = a.filter(function(item, pos, arr){
// Always keep the 0th element as there is nothing before it
// Then check if each element is different than the one before it
return pos === 0 || item !== arr[pos-1];
});

document.getElementById('result').innerHTML = b.join(', ');
<p id="result"></p>

if you are looking purely by algorithm without using any function

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5];

function identical(array){

var newArray = [];
newArray.push(array[0]);
for(var i = 0; i < array.length -1; i++) {
if(array[i] != array[i + 1]) {
newArray.push(array[i + 1]);
}
}
console.log(newArray);
}
identical(arr);

Yet another way with reduce

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5];

var result = arr.reduce(function(acc, cur) {
if (acc.prev !== cur) {
acc.result.push(cur);
acc.prev = cur;
}
return acc;
}, {
result: []
}).result;

document.getElementById('d').innerHTML = JSON.stringify(result);
<div id="d"></div>

A bit hackey, but, hell, I like it.

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5];
var arr2 = arr.join().replace(/(.),(?=\1)/g, '').split(',');

Gives you

[5,2,9,4,5]

Admittedly this will fall down if you're using sub-strings of more than one character, but as long as that's not the case, this should work fine.

Try this:

var a = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4, 5, 5, 5];

uniqueArray = a.filter(function(item, pos) {
return a.indexOf(item) == pos;
});