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Sep 2, 2015 · Easiest way to find duplicate values in a javascript array. How do I check if an array has duplicate values? If some elements in the array are the same, then return true. Otherwise, return false. ['hello','goodbye','hey'] //return false because no duplicates exist ['hello','goodbye','hello'] // return true because duplicates exist
- 12 min
- Using Nested For In Loop. In the loop, we will give each index of the array to iterate, and in each iteration, we are checking that the element at any iteration is the same or not; if they are the same, then we add it to duplicated_elements, and if iterations are the same, then we skip it.
- Using Sort() Method. This array.sort() method is provided by Javascript by which we can sort our array, and after sorting the array, we are checking that the element at the last index is the same or not; if they are the same, it means it’s a duplicate element.
- Using filter() Method. The array filter() method returns elements of the array that pass the condition of the array and forms a new array by using these elements, and here we are checking whether a particular element has two different indexes or not; if they do, they are duplicate elements.
- Using a Set. A data structure is said to be a set when no elements repeat in it. Here, we are checking whether a particular element exists in the set or not.
- Set Object
- IndexOf() Method
- Some() Method
- For Loop
Set is a special data structure introduced in ES6 that stores a collection of unique values. Since each value in a Sethas to be unique, passing any duplicate item will be removed automatically: The Array.from() method, we used above, converts the Set back to an array. This is required because a Setis not an array. You could also use spread operator...
In this method, we compare the index of the first occurrence of an element with all the elements in an array. If they do not match, it implies that the element is a duplicate: The above solution works perfectly as long as you only want to check if the array contains repeated items. However, the output array may contain duplicate items if those item...
In JavaScript, the some() method returns trueif one or more elements pass a certain condition. Just like the filter() method, the some()method iterates over all elements in an array to evaluate the given condition. In the callback function, we again use the indexOf()method to compare the current element index with other elements in the array. If bo...
Finally, the last method to find duplicates in an array is to use the for loop. Here is an example that compares each element of the array with all other elements of the array to check if two values are the same using nested for loop: ✌️ Like this article? Follow me onTwitterand LinkedIn.You can also subscribe toRSS Feed.
- Using indexOf() and lastIndexOf() Another way to find duplicate elements in an array is by using the indexOf() and lastIndexOf() methods. For each element in the array, check if the first index of the element is equal to the last index of the element, if not, then it is a duplicate element.
- Using filter() and includes() You can also filter out the duplicate elements from an array using the filter() method. For each element in the array, check if the element is already present in the new array or not, if not, then add it to the new array.
- Using forEach() and includes() This is the same as using for loop, you need to go through each element in the array and check if the element is already present in the new array or not, if not, then add it to the new array.
- Using reduce() and includes() The reduce() method executes a function on each element of the array, that results in a single output value of the array.
May 8, 2009 · Find duplicate values in an array. This should be one of the shortest ways to actually find duplicate values in an array. As specifically asked for by the OP, this does not remove duplicates but finds them.
- You could sort the array and then run through it and then see if the next (or previous) index is the same as the current. Assuming your sort algori...
- If you want to elimate the duplicates, try this great solution: function eliminateDuplicates(arr) { var i, len = arr.length, out = [], ob...
- This is my answer from the duplicate thread (!): When writing this entry 2014 - all examples were for -loops or jQuery. JavaScript has the perfect...
- UPDATED: Short one-liner to get the duplicates: [1, 2, 2, 4, 3, 4].filter((e, i, a) => a.indexOf(e) !== i) // [2, 4] To get the array without dupl...
- Find duplicate values in an array This should be one of the shortest ways to actually find duplicate values in an array. As specifically asked for...
- You can add this function, or tweak it and add it to Javascript's Array prototype: Array.prototype.unique = function () { var r = new Array();...
- UPDATED: The following uses an optimized combined strategy. It optimizes primitive lookups to benefit from hash O(1) lookup time (running unique on...
- var a = ["a","a","b","c","c"]; a.filter(function(value,index,self){ return (self.indexOf(value) !== index )})
- Find non-unique values from 3 arrays (or more): ES2015 // 🚩🚩 🚩 🚩 🚩 var arr = [1,2,2,3,3,4,5,6,2,3,7,8,5,22], arr2 = [1,2,511,12,...
Mar 14, 2022 · To find duplicates in an array using JavaScript, the Set object combined with the has() method offers an effective solution. A Set is a collection of unique values, and the has() method determines whether a Set object contains a specified element.
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Mar 2, 2024 · This is a three-step process: Use the Array.some() method to iterate over the array. Check if the index of the first occurrence of the current value is NOT equal to the index of its last occurrence. If the condition is met, then the array contains duplicates. index.js.
