问题
I am working with Geofire and Firebase on Angular 6 to store locations and unfortunately it's storing a lot of duplicates this is an example (console logging my variable currentHits):
0: {location: Array(2), distance: "48.84", url: "assets/imgs/fix.png"}
1: {location: Array(2), distance: "48.84", url: "assets/imgs/fix.png"}
2: {location: Array(2), distance: "48.84", url: "assets/imgs/fix.png"}
3: {location: Array(2), distance: "48.85", url: "assets/imgs/free.png"}
4: {location: Array(2), distance: "48.85", url: "assets/imgs/free.png"}
5: {location: Array(2), distance: "48.85", url: "assets/imgs/free.png"}
6: {location: Array(2), distance: "48.87", url: "assets/imgs/low.png"}
7: {location: Array(2), distance: "48.87", url: "assets/imgs/low.png"}
8: {location: Array(2), distance: "48.87", url: "assets/imgs/low.png"}
Location basically is an array of latitude and longitude used to calculate distance, in id 0, 1 and 2 its the same coordinates, and 3,4 and 5 are also the same, ...
This is what I want to get:
0: {location: Array(2), distance: "48.84", url: "assets/imgs/fix.png"}
1: {location: Array(2), distance: "48.85", url: "assets/imgs/free.png"}
2: {location: Array(2), distance: "48.87", url: "assets/imgs/low.png"}
(Optional) this is how It stores these locations:
...
hits = new BehaviorSubject([])
...
queryHits(...){
....
let hit = {
location: location,
distance: distance.toFixed(2),
url:img
}
let currentHits = this.hits.value
currentHits.push(hit)
this.hits.next(currentHits)
....
}
It's true that this question has probably already been asked and I have been digging through all the similar questions and found these functions:
1. RemoveDuplicates()
function removeDuplicates(arr){
let unique_array = []
for(let i = 0;i < arr.length; i++){
if(unique_array.indexOf(arr[i]) == -1){
unique_array.push(arr[i])
}
}
return unique_array
}
var newlist = removeDuplicates(list)
It didn't work I get the same list with duplicates.
2. arrUnique:
function arrUnique(arr) {
var cleaned = [];
arr.forEach(function(itm) {
var unique = true;
cleaned.forEach(function(itm2) {
if (_.isEqual(itm, itm2)) unique = false;
});
if (unique) cleaned.push(itm);
});
return cleaned;
}
var newlist= arrUnique(list);
Also, it didn't work..
3. onlyUnique
onlyUnique(value, index, self) {
return self.indexOf(value) === index;
}
var newlist = list.filter(onlyUnique)
Unfortunately it didn't work...
These are some of the answers given to similar problem to remove duplicates from an array and none of them worked. I don't understand why they won't work for my type of array, If anyone has an idea or knows why would be very helpful.
回答1:
You could use a set to store and check for duplicate values.
const removeDuplicates = arr => {
let matches = new Set();
return arr.filter(elem => {
const {distance} = elem;
if(matches.has(distance)){
return false;
} else {
matches.add(distance);
return true;
}
})
}
Bear in mind that using this approach you may remove results where the distance is the same but the co-ordinates differ. If that causes an issue for you then you'd need to also check against the lat/lng pair.
回答2:
Problem here is comparing Objects. Two objects are never equal unless both are referencing to same Object.
Example:
{} === {} // false
// Two objects are equal only if they are referencing to same object
var a = {};
a === a; // true
It is clear from your problem that you are facing the first case. Among the solutions you tested Solution 1 and Solution 3 are failing because of this reason as indexOf does === comparision.
But Solution 2 should have worked on your example as it does a deep comparision as explained here. https://lodash.com/docs#isEqual.
PS: It might be a simple typo i have observed in Solution 2 cleaned.,push(itm);, there is an extra comma. Hoping that is not the case I am moving ahead
So i guess the issue is inside your location array, if you can give the contents of location array we should be able to provide better solution. Or as others suggested you can filter based on a single key of the object like id or distance, instead of comparing the whole object
回答3:
You can use following approach:
Idea:
- You can create your own data structure and have a hashMap to save values.
- Since you have location data, you can use
longitude|latitudeas your key name as it will be unique. - Then expose some functions say,
addthat will check if value exists, override else add. - Also create a property, say
valuethat would return the list of locations.
Note: Above behavior can be achieved using Set as well. If you cannot use ES6 features, then this is one way that is extensible and easy.
function MyList() {
var locations = {};
this.add = function(value) {
var key = value.location.join('|');
locations[key] = value;
}
Object.defineProperty(this, 'value', {
get: function() {
return Object.keys(locations).map(function(key) {return locations[key] })
}
})
}
var locations = new MyList();
locations.add({location: [123.12, 456.23], name: 'test 1' });
locations.add({location: [123.16, 451.23], name: 'test 2' });
locations.add({location: [123.12, 456.23], name: 'test 1' });
locations.add({location: [100.12, 456.23], name: 'test 3' });
locations.add({location: [123.12, 456.23], name: 'test 1' });
locations.add({location: [123.12, 400.23], name: 'test 4' });
console.log(locations.value)Typescript version for more readability:
interface ILocation {
location: Array<number>
[key: string]: any;
}
interface IList {
[key: string]: ILocation
}
class MyList {
private locations: IList = {};
public add(value: ILocation) {
const key: string = value.location.join('|');
this.locations[key] = value;
}
public get value(): Array<ILocation> {
return Object.keys(locations).map(function(key) {return locations[key] })
}
}
回答4:
uniqWith https://lodash.com/docs/#uniqWith can be used to specify the method to compare by :
var arr = [ { location: [1, 2], distance: "48.84", url: "assets/imgs/fix.png" },
{ location: [1, 2], distance: "48.84", url: "assets/imgs/fix.png" },
{ location: [1, 2], distance: "48.84", url: "assets/imgs/fix.png" },
{ location: [3, 4], distance: "48.85", url: "assets/imgs/free.png"},
{ location: [3, 4], distance: "48.85", url: "assets/imgs/free.png"},
{ location: [3, 4], distance: "48.85", url: "assets/imgs/free.png"},
{ location: [5, 6], distance: "48.87", url: "assets/imgs/low.png" },
{ location: [5, 6], distance: "48.87", url: "assets/imgs/low.png" },
{ location: [5, 6], distance: "48.87", url: "assets/imgs/low.png" } ]
var result = _.uniqWith(arr, (a, b) => _.isEqual(a.location, b.location));
console.log( JSON.stringify({...result}).replace(/},/g, '},\n ') );<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.11/lodash.min.js"></script>回答5:
You could always check before you add the hits to make sure there are no repeats.
edit: You cannot compare objects unless they have the same reference object. So, you could compare objects by a unique ID
use rxjs filter() this will return an array
// store history of objs for comparison
addedObjs = [];
this.hits.pipe(filter(obj => {
// check if id is an index of the previous objs
if (addObjs.indexOf(obj.id) === -1) {
this.addedObjs.push(obj.id)
return obj
});
here is the working stackblitz using some of your code
回答6:
Perhaps you would want to use a library such as lodash which has a wide set of functions regarding all types of collections.
let newArr = _.uniqWith(myArr, _.isEqual);
uniqWith with the help of isEqual can get what you want.
Here is fiddle to that solution
回答7:
I think it is your comparison that may not be working correctly. You can try this:
var uniqueHits = currentHits.reduce((acc, curr) => {
if (acc.length === 0) {
acc.push(curr);
} else if (!acc.some((item) =>
item.location[0] === curr.location[0]
&& item.location[1] === curr.location[1]
&& item.distance === curr.distance
&& item.url === curr.url)) {
acc.push(curr);
}
return accumulator;
}, []);;
来源：https://stackoverflow.com/questions/52480479/remove-duplicates-from-an-array-of-geofire-objects