How to compare each object in an array with each other. When found update the object with a new property

Question

For example consider the following array with objects.

var collection = [{name:'user1',phone:'203'},
                  {name:'user2',phone:'5050'},
                  {name:'user1',phone:'203'}]

Now I want to compare the each object with each other and give the result as.

var newCollection =   {name:'user1',phone:'203', rowMatch:'true'},
                      {name:'user2',phone:'5050', rowMatch:'false'},
                      {name:'user1',phone:'203',rowMatch:'true'}

So, I want the new collecition like this where it compares and updates with new property when object properties match like the first and third object.

you mean if 2 or more rows are same, you need to set the `rowMatch` to true ? — Dane, Nov 07 '17 at 17:22
Even if one row matches with another you have to update both the object with rowMatch : true. — Ajay, Nov 07 '17 at 19:11

score 1 · Answer 1 · answered Nov 07 '17 at 17:30

var newCollection = collection.map(item => {
   item.rowMatch = !!collection.find(i => i !== item && i.phone === item.phone && i.name === item.name);
   return item;
});

Here you're just using map to iterate through and check if each item has a duplicate that isn't the original.

score 0 · Answer 2 · answered Nov 07 '17 at 17:26

0

Create a hash function for your object type.

A simple concatenation of the fields seems to work in this case. Iterate through your collection and for each element, hash it, and put it in a table.

Keep track of the counts. When the count is greater than 1 you know you have a duplicate (row match)

JavaScript Hashmap Equivalent

answered Nov 07 '17 at 17:26

WillW

43
6

then he'll need to go back through to assign the property to the previous item – bryan60 Nov 07 '17 at 17:27
A simple concat could produce false positives. – Rick Jolly Nov 07 '17 at 17:28

DesTroy · Answer 3 · 2017-11-07T17:35:24.223

0

use Array.prototype.find

var newCollection = collection.map((row, index) => {
       if(row["rowMatch"])
          return row; 

      rowMatch = !!collection.find((r,i) => i !== index && r.name === row.name && r.phone === row.phone); 
      row["rowMatch"] = rowMatch;

      return row; 

})

edited Nov 07 '17 at 17:35

answered Nov 07 '17 at 17:29

DesTroy

390
4
17

this will always find the item you're currently on, need to exclude it. and your find usage is off, find doesn't return -1 if not found, it returns undefined. – bryan60 Nov 07 '17 at 17:32
@bryan60, yup saw that now, returns `undefined`, using double not now. – DesTroy Nov 07 '17 at 17:36

Touqeer · Accepted Answer · 2017-11-07T18:40:29.990

0

You can use newCollection or manipulate in the collection like this

collection.forEach((item)=>{
item.rowMatch = (collection.filter((e)=>{return (e.name==item.name&&e.phone==item.phone)}).length>1)?'true':'false';
})
console.log(collection)

Simple is that.Here is working JSFiddle for it https://jsfiddle.net/touqeer/pgdsw9Le/1/ .

edited Nov 07 '17 at 18:40

answered Nov 07 '17 at 17:59

Touqeer

150
1
10

@Rick Jolly No this will not.You can see working fiddle in edited answer now.Thanks – Touqeer Nov 07 '17 at 18:24
Find will not let you know the length.The basic logic is to find more iteration of an object. – Touqeer Nov 07 '17 at 18:25
My bad, didn't notice the `length > 1`. Deleted my comments to avoid confusion. – Rick Jolly Nov 07 '17 at 18:29
Thanks man.If you have tried this then upvote.Thanks in advance. – Touqeer Nov 07 '17 at 18:31
Yeah it works but would rather see `item.rowMatch = (condition)` or `item.rowMatch = (condition) ? 'true' : 'false'` if strings are necessary. I also don't prefer the filter inefficiency and direct mutation though. – Rick Jolly Nov 07 '17 at 18:37
this is less performant for an already poor performance operation, filter demands that you continue checking even after a match is found rather than stopping when 2 are found. Find should be used instead. – bryan60 Nov 07 '17 at 18:41
Answer updated as you want but i think filter have to be there as we would have to iterate on all items for taking length of matched items – Touqeer Nov 07 '17 at 18:41
this method works, but it is worse performance than using find. The big O with this method is always n^2, with a find operation instead, the big O is significantly lower. – bryan60 Nov 07 '17 at 18:43
Find gets the value of the first element in the array that has a matched value. – Touqeer Nov 07 '17 at 18:45
Thanks @Ajay you are awesome.If this was helpful than please accept the answer and give it an upvote.Thanks again man. – Touqeer Nov 07 '17 at 18:47
yes, which is why you just need to add a simple check to make sure you're not looking at the same object. Then it stops iterating after it finds a match that isn't the current object. Much better performance. Your method does needless iteration. – bryan60 Nov 07 '17 at 19:09

How to compare each object in an array with each other. When found update the object with a new property

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