组合阵列以消除重复项的最有效方法

Question

Using a Flatlist and looking for an efficient way to combine elements of a list, while removing the duplicate elements. Each element has a unique key value, to know whether it is a duplicate or not.

My current implimentation uses the concat function:

Array.prototype.unique = function() {
      var a = this.concat();
      for(var i=0; i<a.length; ++i) {
          for(var j=i+1; j<a.length; ++j) {
              if(a[i].key === a[j].key)
                  a.splice(j--, 1);
          }
      }
      return a;
  };

const OldArray = this.state.data;
const NewArray = [] //contains values we loaded in 
const FinalArray = OldArray.concat(NewArray).unique();

//Update the State
this.setState({
   data: FinalArray
)}

This definitely works, but every time this function runs its at least N^2 efficiency, which seems bad. Is there a better way to do this? I feel like there must be..

Answer 1

You can use Array#reduce to creae a Map of unique values, and then spread it back to an array. This will get you the 1st appearance of the objects that have the same key.

 const union = (arr1, arr2, key) => [... // spread to an array arr1.concat(arr2) // concat the arrays .reduce((m, o) => m.has(o[key]) ? m : m.set(o[key], o), new Map) // reduce to a map by value of key .values()]; // get the values iterator const OldArray = [{ a: 1, v: 1 }, { a: 2 }] const NewArray = [{ a: 1, v: 100 }, { a: 3 }] const FinalArray = union(OldArray, NewArray, 'a') console.log(FinalArray); 

The other option, as suggested by @4castle, is to use Array#map to initialize the Map. However, this will take the last appearance of the objects that have the same key. You can always Array#reverse the array before initializing the Map.

 const union = (arr1, arr2, key) => [... // spread to an array new Map(arr1.concat(arr2).map(o => [o[key], o])) // concat and initialize the map .values()]; // get the values iterator const OldArray = [{ a: 1, v: 1 }, { a: 2 }] const NewArray = [{ a: 1, v: 100 }, { a: 3 }] const FinalArray = union(OldArray, NewArray, 'a') console.log(FinalArray);