咱們在實際工做中,或者在面試找工做時,都會用到或者被問到一個問題,那就是「數組如何去重」。是的,這個問題有不少種解決方案,看看下面的十種方式吧!面試
function unique(arr){ var res = [arr[0]]; for(var i=1; i<arr.length; i++){ var repeat = false; for(var j=0; j<res.length; j++){ if(arr[i] === res[j]){ repeat = true; break; } } if(!repeat){ res.push(arr[i]); } } return res; } console.log('------------方法一---------------'); console.log(unique([1,1,2,3,5,3,1,5,6,7,4]));
function unique2(arr){ var arr2 = arr.sort(); var res = [arr2[0]]; for(var i=1; i<arr2.length; i++){ if(arr2[i] !== res[res.length-1]){ res.push(arr2[i]); } } return res; } console.log('------------方法二---------------'); console.log(unique2([1,1,2,3,5,3,1,5,6,7,4]));
function unique3(arr){ var res = []; var obj = {}; for(var i=0; i<arr.length; i++){ if( !obj[arr[i]] ){ obj[arr[i]] = 1; res.push(arr[i]); } } return res; } console.log('------------方法三---------------'); console.log(unique3([1,1,2,3,5,3,1,5,6,7,4]));
function unique4(arr){ var res = []; for(var i=0; i<arr.length; i++){ if(res.indexOf(arr[i]) == -1){ res.push(arr[i]); } } return res; } console.log('------------方法四---------------'); console.log(unique4([1,1,2,3,5,3,1,5,6,7,4]));
function unique5(arr){ var res = []; for(var i=0; i<arr.length; i++){ if( !res.includes(arr[i]) ){ // 若是res新數組包含當前循環item res.push(arr[i]); } } return res; } console.log('------------方法五---------------'); console.log(unique5([1,1,2,3,5,3,1,5,6,7,4]));
function unique6(arr){ var res = []; res = arr.filter(function(item){ return res.includes(item) ? '' : res.push(item); }); return res; } console.log('------------方法六---------------'); console.log(unique6([1,1,2,3,5,3,1,5,6,7,4]));
function unique7(arr){ var res = []; arr.forEach(function(item){ res.includes(item) ? '' : res.push(item); }); return res; } console.log('------------方法七---------------'); console.log(unique7([1,1,2,3,5,3,1,5,6,7,4]));
function unique8(arr){ var i, j, len = arr.length; for(i = 0; i < len; i++){ for(j = i + 1; j < len; j++){ if(arr[i] == arr[j]){ arr.splice(j,1); len--; j--; } } } return arr; } console.log('------------方法八---------------'); console.log(unique8([1,1,2,3,5,3,1,5,6,7,4]));
function unique9(arr){ var res = []; for(var i=0; i<arr.length; i++){ res.lastIndexOf(arr[i]) !== -1 ? '' : res.push(arr[i]); } return res; } console.log('------------方法九---------------'); console.log(unique9([1,1,2,3,5,3,1,5,6,7,4]));
function unique10(arr){ //Set數據結構,它相似於數組,其成員的值都是惟一的 return Array.from(new Set(arr)); // 利用Array.from將Set結構轉換成數組 } console.log('------------方法十---------------'); console.log(unique10([1,1,2,3,5,3,1,5,6,7,4]));
有意思的是,當我把數組的長度變得很大的時候(以下所示),測試了一下不一樣方法的執行時間長短,會發現方法3、4、5、6、七相對來講會更有優點,而方法八的執行速度彷佛一直墊底。你也能夠在你本地跑一下試試!數組
//測試用的超大數組 var arr = 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//這裏只是舉例方法三(若是你把全部方法放在一塊兒測試,會更直觀的看到執行時間的差別) var time3 = new Date().getTime(); function unique3(arr){ var res = []; var obj = {}; for(var i=0; i<arr.length; i++){ if( !obj[arr[i]] ){ obj[arr[i]] = 1; res.push(arr[i]); } } return res; } console.log('------------方法三---------------'); console.log( unique3(arr) ); console.log('3所花時間: ' + (new Date().getTime() - time3));