Need to filter one array based on another array. Is there a util function in knock out ? else i need to go with javascript
First :
var obj1 = [{
"visible": "true",
"id": 1
}, {
"visible": "true",
"id": 2
}, {
"visible": "true",
"id": 3
}, {
"Name": "Test3",
"id": 4
}];
Second :
var obj2 = [ 2,3]
Now i need to filter obj1 based on obj2 and return items from obj1 that are not in obj2 omittng 2,3 in the above data (Comparison on object 1 Id)
output:
[{
"visible": "true",
"id": 1
}, {
"Name": "Test3",
"id": 4
}];
3 Answers
You can simply run through obj1 using filter and use indexOf on obj2 to see if it exists. indexOf returns -1 if the value isn't in the array, and filter includes the item when the callback returns true.
var arr = obj1.filter(function(item){
return obj2.indexOf(item.id) === -1;
});
With newer ES syntax and APIs, it becomes simpler:
const arr = obj1.filter(i => !obj2.includes(i.id))
Even if the answer provided by @Joseph are good, it can lead to performance issues if you have a very large array. The complexity is O(n^2), but it can be improved to O(n). Below I put the code I'd use to perform this task:
//create a map for storing object id
const map = new Map();
//add existing id from the array to the map
for (item of obj2) {
map.set(item.id, true);
}
//create a new array that contains all items that aren't included in the //map
//the map lookUp is O(1) complexity
const arr = obj1.filter(item => !map[item.id]);
In this way we avoid nested iteration and have O(n) complexity
To create your output array, create a function that will iterate through obj1 and populate a new array based on whether the id of every obj in the iteration exists in obj2.
var obj1 = [{
"visible": "true",
"id": 1
}, {
"visible": "true",
"id": 2
}, {
"visible": "true",
"id": 3
}, {
"Name": "Test3",
"id": 4
}];
var obj2 = [2,3]
var select = function(arr) {
var newArr = [];
obj1.forEach(function(obj) {
if obj2.indexOf(obj.id) !== -1 {
newArr.push(obj)
};
};
return newArr;
};
