Explore how to remove duplicate values from JavaScript arrays and strings

  • 2021-01-25 07:08:47
  • OfStack

The principle is very clear in the code, so let's go straight to the code example:


var ages = array.map(function(obj) { return obj.age; }); 
ages = ages.filter(function(v,i) { return ages.indexOf(v) == i; }); 
 
console.log(ages); //=> [17, 35] 

function isBigEnough(element) { 
 return element >= 10; 
} 
var filtered = [12, 5, 8, 130, 44].filter(isBigEnough); 
// filtered is [12, 130, 44] 


function onlyUnique(value, index, self) {  
  return self.indexOf(value) === index; 
} 
 
// usage example: 
var a = ['a', 1, 'a', 2, '1']; 
var unique = a.filter( onlyUnique ); // returns ['a', 1, 2, '1'] 

Better Function(not compatible with IE7)


function unique(array){ 
  return array.filter(function(el, index, arr) { 
    return index == arr.indexOf(el); 
  }); 
} 


Function(compatible with IE7)


// Remove duplicate values from the array  
function getNoRepeat(s) { 
  return s.sort().join(",,").replace(/(,|^)([^,]+)(,,\2)+(,|$)/g,"$1$2$4").replace(/,,+/g,",").replace(/,$/,"").split(","); 
} 
 
var arr = [" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", 
" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", 
" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan "]; 
arr = getNoRepeat(arr); 
 
alert(arr.length);// 4 
alert(arr.toString()); // " Beijing ", " Shanghai ", " tianjin ", " wuhan " 

Using map principle


var arr = [" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", 
" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", 
" Beijing ", " Shanghai ", " tianjin ", " wuhan ", " Shanghai ", " tianjin ", " wuhan ", " Beijing ", " Shanghai ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan ", " tianjin ", " wuhan "]; 
 
var json = {}; 
for(var i = 0; i < arr.length; i++){ 
  json[arr[i]] = arr[i]; 
} 
 
arr = new Array(); 
for(var key in json){ 
  arr.push(key); 
} 
alert(arr.toString()); 
// " Beijing ", " Shanghai ", " tianjin ", " wuhan " 


Related articles: