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Filtering an array of values by array of object's value

In Javascript we have an array:
let arr1 = [1, 2, 3, 4, 5];
...and an array of objects:
let arr2 = [ {name: "banana", id: 1},
{name: "mango", id: 3} ];
I want to remove all the elements from arr1 where arr2's id = arr1's value and return an array like this:
[2, 4, 5]
Here is what I've tried, but it doesn't seem to work.
let newArr = arr1.filter(
x => !arr2.includes(e => e.id === x)
)
How can I achieve this? I can use lodash as well as ES6.

The .includes() method doesn't allow you to pass a method into it to define equality. You can use .some() instead, which does allow you to specify this:
const arr1 = [1, 2, 3, 4, 5];
const arr2 = [
{name: "banana", id: 1},
{name: "mango", id: 3}
];
const newArr = arr1.filter(x => !arr2.some(e => e.id === x))
console.log(newArr);
A more efficient approach would be to grab all the id properties from the objects in your array and put then in a Set for quick look-up. Then use .filter() with .has() like so:
const arr1 = [1, 2, 3, 4, 5];
const arr2 = [
{name: "banana", id: 1},
{name: "mango", id: 3}
];
const idSet = new Set(arr2.map(({id}) => id));
const newArr = arr1.filter(x => !idSet.has(x))
console.log(newArr);

You can first create a temporary of id and age, then use filter() with includes()
let arr1 = [1, 2, 3, 4, 5];
let arr2 = [ {name: "banana", id: 1},
{name: "mango", age: 3} ];
let temp = arr2.map(i => i.id || i.age);
let res = arr1.filter(i => !temp.includes(i));
console.log(res);

let arr1 = [1, 2, 3, 4, 5];
let arr2 = [ {name: "banana", id: 1},
{name: "mango", id: 3} ];
arr1.map((item,index) =>
arr2.map(object => {
if(item == object.id) arr1.splice(index,1)
})
)
console.warn(arr1) /// output [2, 4, 5]

how do i convert array of one object containing many object inside to array of object

I have an array looks like below...
arr = [{
Bildbearbeiter: 1,
Bügler: 2,
Einkäufer: 3,
Empfänger: 4,
Fotograf: 5,
}];
but I want to change it
arr = [{
Bildbearbeiter: 1
},
{
Bügler: 2
},
{
Einkäufer: 3
},
{
Empfänger: 4
},
{
Fotograf: 5
}
];
So that i can iterate with each object. Is there any way to solve it??
Thanks in advance

Use Array.map and Object.entries
let arr = [{Bildbearbeiter: 1,Bügler: 2,Einkäufer: 3,Empfänger: 4,Fotograf: 5}];
arr = Object.entries(arr[0]).map(([k,v]) => ({[k]:v}));
console.log(arr);

You can simply use Array.map() and Object.keys():
let arr = [ { Bildbearbeiter: 1, Bügler: 2, Einkäufer: 3, Empfänger: 4, Fotograf: 5, } ];
let result = Object.keys(arr[0]).map((key)=> ({[key] : arr[0][key]}));
console.log(result);

Try this by clicking on Run code snippet button:
var arr = [{
Bildbearbeiter: 1,
Bügler: 2,
Einkäufer: 3,
Empfänger: 4,
Fotograf: 5,
}];
var newArray = [];
for (let key in arr[0]) {
newArray.push({
[key]: arr[0][key]
});
}
console.log(newArray);
Or try this:
var arr = [{
Bildbearbeiter: 1,
Bügler: 2,
Einkäufer: 3,
Empfänger: 4,
Fotograf: 5,
}];
var newArray = Object.keys(arr[0]).map(key => ({
[key]: arr[0][key]
}))
console.log(newArray);

You could reduce the array by adding all objects to the result set.
var array = [{ "Bildbearbeiter": 1, "Bügler": 2, "Einkäufer": 3, "Empfänger": 4, "Fotograf": 5 }],
result = array.reduce((r, o) => r.concat(Object.entries(o).map(([k, v]) => ({ [k]: v }))), []);
console.log(result);

You can map the array, loop through the keys of each object, and assign a brand new object holding the key and the value of the current item.
arr.map(i => {
return Object.keys(i).map(k => {
return {[k]: i[k]};
});
});
Working fiddle: http://jsfiddle.net/sw3Lxm7f/

Convert two arrays into an object

var foo = { "a": [1,2,3] }
var bar = { "b": [7,8,9] }
output should look like this
[ {a: 1, b: 7}, {a: 2, b: 8}, {a:3, b: 9}]
How can I do this using ramda or javascript functional programming ?
I have done this using for loop i = 0, is it possible using functional ramda programming

If both arrays are always the same length, you can do this using map.
function mergeArrays(arr1, arr2) {
return arr1.map(function(item, index) {
return {
a: arr1[index], //or simply, item
b: arr2[index]
};
});
}
var a = [1, 2, 3];
var b = [7, 8, 9];
var joined = mergeArrays(a, b);
document.getElementById('result').innerHTML = JSON.stringify(joined, null, 2);
<pre id="result">
</pre>

You can achieve this using R.transpose to convert an array of [[1,2,3], [7,8,9]] to [[1, 7], [2, 8], [3, 9]] and then map over it with R.zipObj.
const fn = R.compose(
R.map(R.zipObj(["a", "b"])),
R.transpose
)
const a = [1, 2, 3], b = [7, 8, 9]
const result = fn([a, b])
console.log(result)
<script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script>
If you would prefer to pass a and b as two arguments to fn rather than an array then you can swap R.transpose in the example above with R.unapply(R.transpose).

Assuming you want [{a:1,b:7},{a:2,b:8},{a:3,b:9}] it can be done pretty easily with map using the index to get the value in b:
var result = a.map((v, i) =>({ a: v, b: b[i] }));

i am having an array
const peopleObject = { "123": { id: 123, name: "dave", age: 23 },
"456": { id: 456, name: "chris", age: 23 }, "789": { id: 789, name:
"bob", age: 23 }, "101": { id: 101, name: "tom", age: 23 }, "102":
{ id: 102, name: "tim", age: 23 } }
for this particular i have created a code that convrts array to object i hope this is usefull for you
const arrayToObject = (array) =>
array.reduce((obj, item) => {
obj[item.id] = item
return obj
}, {})
const peopleObject = arrayToObject(peopleArray)
console.log(peopleObject[idToSelect])

Your expected output doesn't have a valid format. You should store the data in array. Like ,
var output = [];
var a = [1,2,3], b = [7,8,9];
for(var i=0; i< a.length; i++){
var temp = {};
temp['a'] = a[i];
temp['b'] = b[i];
output.push(temp);
}
You cannot store the result in an object the way you want. Objects are key-value pairs. But what you expect is only the values without keys which is not possible!

create function form ramda's addIndex and map
const data = { keys: ['a', 'b', 'c'], values: ['11', '22', '33'] }
const mapIndexed = R.addIndex(R.map)
const result = mapIndexed((item, i) => {
return { [item]: data.values[i] }
}, data.keys)
You will get an array of objects

How to remove the same object in two arrays with lodash or underscore?

Now I have two object arrays,
var arr1 = [{id: 0, name: 'Jack'}, {id: 1, name: 'Ben'}, {id: 2, name: 'Leon'}, {id: 3, name: 'Gavin'}];
var arr2 = [{id: 0, name: 'Jack'}, {id: 5, name: 'Jet'}, {id: 2, name: 'Leon'}];
I want to remove those objects of same id in arr1 and arr2, so the results are:
var arr1 = [{id: 1, name: 'Ben'}, {id: 3, name: 'Gavin'}];
var arr2 = [{id: 5, name: 'Jet'}];
How to implement it with lodash or underscore?
Here are my implementation.
arr1_ids = _.pluck(arr1, 'id');
arr2_ids = _.pluck(arr2, 'id');
same_ids = _.intersection(arr1_ids, arr2_ids);
arr1 = _.remove(arr1, function(e) { return !_.contains(same_ids, e.id); });
arr2 = _.remove(arr2, function(e) { return !_.contains(same_ids, e.id); });
Is there any better way to do that?

Can you use _.difference?
same_elements = _.intersection(arr1, arr2);
arr1 = _.difference(arr1, same_elements);
arr2 = _.difference(arr2, same_elements);

I'm not sure how this should be done with underscore or lodash, but here's a JavaScript implementation.
It creates a filter function that you can then apply to both arrays to only keep the elements that aren't part of the intersection.
var arr1 = [{id: 0, name: 'Jack'}, {id: 1, name: 'Ben'}, {id: 2, name: 'Leon'}, {id: 3, name: 'Gavin'}];
var arr2 = [{id: 0, name: 'Jack'}, {id: 5, name: 'Jet'}, {id: 2, name: 'Leon'}];
var negative_intersection_filter = function(a, b) {
// create a map to speed up the filtering later
var map = a.reduce(function(map, current) {
// perform the intersection
map[current.id] = b.some(function(item) {
return item.id == current.id;
});
return map;
}, {});
// our filtering function, simple
return function(item) {
return !map[item.id];
}
}(arr1, arr2);
// apply the filter here
arr1 = arr1.filter(negative_intersection_filter);
arr2 = arr2.filter(negative_intersection_filter);
console.log(arr1);
console.log(arr2);

I think your algorithm is about right, here's a slightly different approach in plain js. I've used a, b instead of arr1, arr2 for brevity:
// Collect ids and sort
var ids = a.map(function(obj) {return obj.id}).concat(b.map(function(obj) {return obj.id})).sort();
// Get IDs that aren't duplicates
var nonDups = ids.filter(function(v, i, o){return v !== o[i-1] && v !== o[i+1]});
// Keep only the non-duplicates in each array
a.reduceRight(function(pre, cur, i, o){if (nonDups.indexOf(cur.id) == -1) o.splice(i, 1)},0);
b.reduceRight(function(pre, cur, i, o){if (nonDups.indexOf(cur.id) == -1) o.splice(i, 1)},0);
JSON.stringify(a) // [{"id":1,"name":"Ben"},{"id":3,"name":"Gavin"}]
JSON.stringify(b) // [{"id":5,"name":"Jet"}]
reduceRight is just used to iterate over each array backwards so that splicing doesn't affect the iteration.

Extract from arrays the common elements in javascript

i have a question about arrays in javascript using jquery and knockout js.
I have this structure in my code:
var MyModel = function(model) {
var self = this;
self.FirstArray = ko.observableArray(ko.utils.arrayMap(model.FirstArray, function(object){
return new ArrayObj(object);
}));
/*--here's the code that i need to implement--*/
}
var ArrayObj = function(obj){
var self = this;
self.VarX = obj.VarX;
self.SeccondArray = ko.observableArray(ko.utils.arrayMap(obj.SeccondArray, function(seccond){
return new Object2(seccond);
}));
}
var Object2 = function(obj2) {
var self = this;
self.IdObj2 = obj2.IdObj2;
self.Name = obj2.Name;
}
The problem is that i need another array, that depends on the items that are in common between the Object2 arrays in SeccondArray.
In an example, its something like this:
Array1 = [{IdObj2: 1, Name: "A"},
{IdObj2: 2, Name: "B"},
{IdObj2: 3, Name: "C"}]
Array2 = [{IdObj2: 1, Name: "A"},
{IdObj2: 3, Name: "C"}]
Array3 = [{IdObj2: 3, Name: "C"}]
FirstArray = [{VarX: J, Array1},
{VarX: K, Array2},
{VarX: L, Array3}]
So.. the array that i need, must have:
ResultArray = [{IdObj2: 3, Name: "C"}]
Because {IdObj2: 2, Name: "C"} it's the only common between them.
I hope you can help me with this.

What you are looking for is an intersection. I used a library called underscore and used a nifty object intersection I found here How to use underscore's "intersection" on objects?
here is the fiddle with it working
http://jsfiddle.net/sujesharukil/vyguB/
_.intersectionObjects = _.intersect = function(array) {
var slice = Array.prototype.slice; // added this line as a utility
var rest = slice.call(arguments, 1);
return _.filter(_.uniq(array), function(item) {
return _.every(rest, function(other) {
return _.any(other, function(element) { return _.isEqual(element, item); });
});
});
};
var Array1 = [{IdObj2: 1, Name: "A"},
{IdObj2: 2, Name: "B"},
{IdObj2: 3, Name: "C"}],
Array2 = [{IdObj2: 1, Name: "A"},
{IdObj2: 3, Name: "C"}],
Array3 = [{IdObj2: 3, Name: "C"}];
var result = _.intersectionObjects(Array1, Array2, Array3);
console.log(result);
Hope that helps.
Cheers!