We Keep Coding

Transform an array of objects by removing object properties not contained in another array

A long title, so I´ll explain the problem by example. I have an array of objects:
const myObjects = [
{
id: 1,
name: "a",
stuff: "x"
},
{
id: 2,
name: "b",
stuff: "y"
},
];
Then I have another array of objects like this:
const myTemplate=[
{
desiredProperty: "name",
someOtherProperty: "..."
},
{
desiredProperty: "stuff",
someOtherProperty: "..."
},
];
Now I want to transform myObjects array to new one, so that the individual objects contain only the properties listed in desiredProperty of each object in myTemplate.
The result should look like this:
myResult = [
{
name: "a",
stuff: "x"
},
{
name: "b",
stuff: "y"
}
]
How to achieve this?

This approach lets you partially apply the template to get back a reusable function to run against multiple sets of inputs:
const convert = (template, keys = new Set (template .map (t => t .desiredProperty))) => (xs) =>
xs .map (
(x) => Object .fromEntries (Object .entries (x) .filter (([k, v]) => keys .has (k)))
)
const myObjects = [{id: 1, name: "a", stuff: "x"}, {id: 2, name: "b", stuff: "y"}]
const myTemplate= [{desiredProperty: "name", someOtherProperty: "..."}, {desiredProperty: "stuff", someOtherProperty: "..."}]
console .log (
convert (myTemplate) (myObjects)
)
But I agree with the comment that the template here is better expressed as an array of keys to keep.

The following code creates a Set of the keys you want to keep. Then, we map over your myObjects array and only keep the object keys that are in the toKeep Set.
const myObjects=[{id:1,name:"a",stuff:"x"},{id:2,name:"b",stuff:"y"}];
const myTemplate=[{desiredProperty:"name",someOtherProperty:"..."},{desiredProperty:"stuff",someOtherProperty:"..."}];
const toKeep = new Set(myTemplate.map(t => t.desiredProperty));
const newObjs = myObjects.map(o => {
const obj = {};
for (let key in o) {
if (toKeep.has(key)) {
obj[key] = o[key];
}
}
return obj;
});
console.log(newObjs);

How to clean empty array objects and renumber them?

I have a JavaScript object like
{0: [], 1: [0: 'a', 1: 'b'], 2: [], 3: [0: '20']}
I want to get rid of the empty slots in this object and renumber the remaining one, so it has a normal order (0, 1, 2).
I use this function:
function clean(obj) {
for (var propName in obj) {
if (obj[propName] === null || obj[propName].length == 0 || obj[propName] === undefined) {
delete obj[propName];
}
}
}
Which clears the object, but then I get
{1: [0: 'a', 1: 'b'], 3: [0: '20']}
But how do I make 1 to 0 and 3 to 1?

First of all, there's a problem with your question since the definition of your first object does not pass JS compilation. The array elements are given a "key" with the index, you wrote... 1: [0: 'a', 1: 'b'] which should be either:
1: {0: 'a', 1: 'b'}
or
1: ['a','b']
You are obviously mixing up between the index of an array, and the keys of an object.
Here you are giving the object keys the name of their index within their array. So perhaps you are asking one of three questions. (I'll answer each):
// 1. Clean [[], ['a','b'], [], '20']
// returning: [['a','b'], ['20']]
// and not using params at all.
// 2. Clean {0: [], 1: ['a','b'], 2: [], 3: ['20']}
// returning: {0: ['a','b'], 1: ['20']}
// 3. Clean {0: {}, 1: {0: 'a', 1: 'b'}, 2: {}, 3: {0: '20'}}
// returning: {0: {0: 'a', 1:'b'}, 1: {0: '20'}}
The fastest way, keeping your function intact, would be to add a new "indexer" at the bottom of your function, correcting the keys. We can use ES6 as follows:
// if to delete...
let oldKey = paramName;
let newKey = (obj.keys().indexOf(oldKey)) - 1;
delete obj[oldKey].assign(o, {[newKey]: o[oldKey] })[oldKey];
This is not very clear.
The clearest way is to use another object and populate the next element only if the original has a value, starting with index zero and increasing it.
function cleanup(obj) {
let newObj = {};
let idx = 0;
for (var propName in obj) {
let prop = obj[propName];
console.log('prop', propName, JSON.stringify(prop))
if (prop !== null
&& prop !== undefined
&& JSON.stringify(prop) != "[]" // not empty array
&& JSON.stringify(prop) !== "{}") { // not empty obj
newObj[idx] = prop;
idx++;
}
}
return newObj;
}
See my JS fiddle which shows this.
You could also use the object's keys() method to get an array of the keynames in the order you would get them from the iterator. For the array you could use the splice(0,idx) to remove that element out.
https://www.w3schools.com/js/js_array_methods.asp
Or you can use the split, but then you have to work "backwards", otherwise the for loop will not work correctly. So first get the propnames, and then work from the last one to the first popping as you go along.

I recommend using an Array instead of an Object, but you could do something like this:
var obj = {0: [], 1: ['a', 'b'], 2: [], 3: ['20']};
var newObj = Object.keys(obj).reduce(function (acc, k) {
var objVal = obj[k];
if (objVal.length) {
acc[Object.keys(acc).length] = objVal;
}
return acc;
}, {});
console.log(newObj);

Assuming arrays as properties, you could filter by length (with a destructuring assignment) and assign this array to an object.
var data = { 0: [], 1: ['a', 'b'], 2: [], 3: ['20'] },
clean = Object.assign({}, Object.values(data).filter(({ length }) => length));
console.log(clean);

Assuming that the index value is implicit
const data = {
0: [],
1: ['a', 'b'],
2: [],
3: ['20']
}
const newData = {};
for (const property in data) {
if (data[property].length !== 0) {
newData[property] = data[property]
}
}
console.log(newData)

This is my suggestion. Also do not use index in array declarations: [0: 'a', 1: 'b'] should be ['a', 'b'].
const data = {0: [], 1: ['a', 'b'], 2: [], 3: ['20']};
const dataArray = Object.values(data);
let result = {};
let index = 0;
dataArray.forEach(d => {
if (d.length) Object.assign(result, {[index++]: d});
})
// result --> {0: ['a', b'], 1: ['20']}

Check if an array contains a specified object

The following function searches an object recursively through an object that has nested arrays:
function findDeep(arr, obj) {
console.log(arr)
if (arr.indexOf(obj) !== -1) {
console.log(arr)
return arr
} else {
arr.forEach(item => {
if (item.children) findDeep(item.children, obj)
})
}
}
const colors = {
children: [
{
name: 'white',
},
{
name: 'yellow',
children: [
{
name: 'black'
}
]
}
]
}
const color = {
name: 'black'
}
findDeep(colors.children, color)
The first console.log(arr) do log the matched array:
[
{ name: 'black' }
]
But he second console.log(arr) doesn't log anything. Shouldn't arr.indexOf(obj) return 1, and therefore make the second console.log(arr) log the array?
Here's the CodePen.

You can not find index of object in array using indexOf unless both the objects(passed in indexOf to test and present in array) are pointing to the same reference.
For example:
var a = {
a: 10
};
var b = [{
a: 10
}, {
b: 20
}];
console.log(b.indexOf(a)); // Object `a` and Object in `0th` index of the array are having similar `key-values`
<script src="http://gh-canon.github.io/stack-snippet-console/console.min.js"></script>
But,
var a = {
a: 10
};
var b = [a, {
b: 20
}];
//`0th` index in the array is nothing but a variable holding `object`
console.log(b.indexOf(a)); //Same variable is tested in `indexOf`
<script src="http://gh-canon.github.io/stack-snippet-console/console.min.js"></script>
From the docs, indexOf() compares searchElement to elements of the Array using strict equality (the same method used by the === or triple-equals operator).
{} === {} will be evaluated as false because,
An expression comparing Objects is only true if the operands reference the same Object. If both operands are objects, then JavaScript compares internal references which are equal when operands refer to the same object in memory.[Ref]
There are few solutions and approaches but all of them will be doing iteration and comparing value of the key in object. Refer this answer

How can I use lodash/underscore to sort by multiple nested fields?

I want to do something like this:
var data = [
{
sortData: {a: 'a', b: 2}
},
{
sortData: {a: 'a', b: 1}
},
{
sortData: {a: 'b', b: 5}
},
{
sortData: {a: 'a', b: 3}
}
];
data = _.sortBy(data, ["sortData.a", "sortData.b"]);
_.map(data, function(element) {console.log(element.sortData.a + " " + element.sortData.b);});
And have it output this:
"a 1"
"a 2"
"a 3"
"b 5"
Unfortunately, this doesn't work and the array remains sorted in its original form. This would work if the fields weren't nested inside the sortData. How can I use lodash/underscore to sort an array of objects by more than one nested field?
I've turned this into a lodash feature request: https://github.com/lodash/lodash/issues/581

Update: See the comments below, this is not a good solution in most cases.
Someone kindly answered in the issue I created. Here's his answer, inlined:
_.sortBy(data, function(item) {
return [item.sortData.a, item.sortData.b];
});
I didn't realize that you're allowed to return an array from that function. The documentation doesn't mention that.

If you need to specify the sort direction, you can use _.orderBy with the array of functions syntax from Lodash 4.x:
_.orderBy(data, [
function (item) { return item.sortData.a; },
function (item) { return item.sortData.b; }
], ["asc", "desc"]);
This will sort first ascending by property a, and for objects that have the same value for property a, will sort them descending by property b.
It works as expected when the a and b properties have different types.
Here is a jsbin example using this syntax.

There is a _.sortByAll method in lodash version 3:
https://github.com/lodash/lodash/blob/3.10.1/doc/README.md#_sortbyallcollection-iteratees
Lodash version 4, it has been unified:
https://lodash.com/docs#sortBy
Other option would be to sort values yourself:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort
function compareValues(v1, v2) {
return (v1 > v2)
? 1
: (v1 < v2 ? -1 : 0);
};
var data = [
{ a: 2, b: 1 },
{ a: 2, b: 2 },
{ a: 1, b: 3 }
];
data.sort(function (x, y) {
var result = compareValues(x.a, y.a);
return result === 0
? compareValues(x.b, y.b)
: result;
});
// data after sort:
// [
// { a: 1, b: 3 },
// { a: 2, b: 1 },
// { a: 2, b: 2 }
// ];

The awesome, simple way is:
_.sortBy(data, [function(item) {
return item.sortData.a;
}, function(item) {
return item.sortData.b;
}]);
I found it from check the source code of lodash, it always check the function one by one.
Hope that help.

With ES6 easy syntax and lodash
sortBy(item.sortData, (item) => (-item.a), (item) => (-item.b))

I think this could work in most cases with underscore:
var properties = ["sortData.a", "sortData.b"];
data = _.sortBy(data, function (d) {
var predicate = '';
for (var i = 0; i < properties.length; i++)
{
predicate += (i == properties.length - 1
? 'd.' + properties[i]
: 'd.' + properties[i] + ' + ')
}
return eval(predicate)
});
It works and you can see it in Plunker

If the problem is an integer is converted to a string, add zeroes before the integer to make it have the same length as the longest in the collection:
var maxLength = _.reduce(data, function(result, item) {
var bString = _.toString(item.sortData.b);
return result > bString.length ? result : bString.length;
}, 0);
_.sortBy(data, function(item) {
var bString = _.toString(item.sortData.b);
if(maxLength > bString.length) {
bString = [new Array(maxLength - bString.length + 1).join('0'), bString].join('');
}
return [item.sortData.a, bString];
});

I've found a good way to sort array by multiple nested fields.
const array = [
{id: '1', name: 'test', properties: { prop1: 'prop', prop2: 'prop'}},
{id: '2', name: 'test2', properties: { prop1: 'prop second', prop2: 'prop second'}}
]
I suggest to use 'sorters' object which will describe a key and sort order. It's comfortable to use it with some data table.
const sorters = {
'id': 'asc',
'properties_prop1': 'desc',//I'm describing nested fields with '_' symbol
}
dataSorted = orderBy(array, Object.keys(sorters).map(sorter => {
return (row) => {
if (sorter.includes('_')) { //checking for nested field
const value = row["properties"][sorter.split('_')[1]];
return value || null;
};
return row[sorter] || null;// checking for empty values
};
}), Object.values(sorters));
This function will sort an array with multiple nested fields, for the first arguments it takes an array to modify, seconds one it's actually an array of functions, each function have argument that actually an object from 'array' and return a value or null for sorting. Last argument of this function is 'sorting orders', each 'order' links with functions array by index. How the function looks like simple example after mapping:
orderBy(array, [(row) => row[key] || null, (row) => row[key] || null , (row) => row[key] || null] , ['asc', 'desc', 'asc'])
P.S. This code can be improved, but I would like to keep it like this for better understanding.

Changing the order of the Object keys....

var addObjectResponse = [{
'DateTimeTaken': '/Date(1301494335000-0400)/',
'Weight': 100909.090909091,
'Height': 182.88,
'SPO2': '222.00000',
'BloodPressureSystolic': 120,
'BloodPressureDiastolic': 80,
'BloodPressurePosition': 'Standing',
'VitalSite': 'Popliteal',
'Laterality': 'Right',
'CuffSize': 'XL',
'HeartRate': 111,
'HeartRateRegularity': 'Regular',
'Resprate': 111,
'Temperature': 36.6666666666667,
'TemperatureMethod': 'Oral',
'HeadCircumference': '',
}];
This is a sample object which i am getting from back end, now i want to change the order of the object. I don't want to sort by name or size... i just want to manually change the order...

If you create a new object from the first object (as the current accepted answer suggests) you will always need to know all of the properties in your object (a maintenance nightmare).
Use Object.assign() instead.
*This works in modern browsers -- not in IE or Edge <12.
const addObjectResponse = {
'DateTimeTaken': '/Date(1301494335000-0400)/',
'Weight': 100909.090909091,
'Height': 182.88,
'SPO2': '222.00000',
'BloodPressureSystolic': 120,
'BloodPressureDiastolic': 80,
'BloodPressurePosition': 'Standing',
'VitalSite': 'Popliteal',
'Laterality': 'Right',
'CuffSize': 'XL',
'HeartRate': 111, // <-----
'HeartRateRegularity': 'Regular', // <-----
'Resprate': 111,
'Temperature': 36.6666666666667,
'TemperatureMethod': 'Oral',
'HeadCircumference': '',
};
// Create an object which will serve as the order template
const objectOrder = {
'HeartRate': null,
'HeartRateRegularity': null,
}
const addObjectResource = Object.assign(objectOrder, addObjectResponse);
The two items you wanted to be ordered are in order, and the remaining properties are below them.
Now your object will look like this:
{
'HeartRate': 111, // <-----
'HeartRateRegularity': 'Regular', // <-----
'DateTimeTaken': '/Date(1301494335000-0400)/',
'Weight': 100909.090909091,
'Height': 182.88,
'SPO2': '222.00000',
'BloodPressureSystolic': 120,
'BloodPressureDiastolic': 80,
'BloodPressurePosition': 'Standing',
'VitalSite': 'Popliteal',
'Laterality': 'Right',
'CuffSize': 'XL',
'Resprate': 111,
'Temperature': 36.6666666666667,
'TemperatureMethod': 'Oral',
'HeadCircumference': '',
}

I wrote this small algorithm which allows to move keys, it's like jQuery .insertAfter() method. You have to provide:
//currentKey: the key you want to move
//afterKey: position to move-after the currentKey, null or '' if it must be in position [0]
//obj: object
function moveObjectElement(currentKey, afterKey, obj) {
var result = {};
var val = obj[currentKey];
delete obj[currentKey];
var next = -1;
var i = 0;
if(typeof afterKey == 'undefined' || afterKey == null) afterKey = '';
$.each(obj, function(k, v) {
if((afterKey == '' && i == 0) || next == 1) {
result[currentKey] = val;
next = 0;
}
if(k == afterKey) { next = 1; }
result[k] = v;
++i;
});
if(next == 1) {
result[currentKey] = val;
}
if(next !== -1) return result; else return obj;
}
Example:
var el = {a: 1, b: 3, c:8, d:2 }
el = moveObjectElement('d', '', el); // {d,a,b,c}
el = moveObjectElement('b', 'd', el); // {d,b,a,c}

You can't order JavaScript object key/value pairs. It's stored in its own internal format, so you should never rely on the order of that. In JS, everything is an Object, even an Array. So sometimes you can introduce bugs when using array notation and object notation together (for x in var)

I like the approved answer by Chamika Sandamal. Here's a simple function that uses their same logic with a little be of freedom to change the order as you need it.
function preferredOrder(obj, order) {
var newObject = {};
for(var i = 0; i < order.length; i++) {
if(obj.hasOwnProperty(order[i])) {
newObject[order[i]] = obj[order[i]];
}
}
return newObject;
}
You give it an object, and an array of the key names you want, and returns a new object of those properties arranged in that order.
var data = {
c: 50,
a: 25,
d: 10,
b: 30
};
data = preferredOrder(data, [
"a",
"b",
"c",
"d"
]);
console.log(data);
/*
data = {
a: 25,
b: 30,
c: 50,
d: 10
}
*/
I'm copying and pasting from a big JSON object into a CMS and a little bit of re-organizing of the source JSON into the same order as the fields in the CMS has saved my sanity.

2020 Update
The answer below was correct at time of writing in 2011. However, since ES6, enumeration order has been specified as part of the language. Here's a nice article summarising this: https://2ality.com/2015/10/property-traversal-order-es6.html
Original answer
Properties of an object in JavaScript do not have an order. There may appear to be an order in some browsers but the ECMAScript specification defines object property enumeration order as being implementation-specific so you should not assume one browser's behaviour will be the same as another's. Chrome, for example, does not use the same ordering as some other browsers: see this lengthy bug report for at least as much discussion of this issue as you could possibly want.
If you need a specific order, use an array, or two arrays (one for keys and one for values).

You can use Object.keys():
var obj = {
a: 1,
b: 2,
c: 4
};
var new_obj = {};
Object.keys(obj)
.sort(function(a, b) {
/** Insert your custom sorting function here */
return a - b;
})
.forEach(function(key) {
new_obj[key] = obj[key];
});
obj = new_obj;

if you want to manually reorder. simply create new object and assign values using old object.
var newObject= [{
'DateTimeTaken': addObjectResponse.DateTimeTaken,
'Weight': addObjectResponse.Weight,
'Height': addObjectResponse.Height,
'SPO2': addObjectResponse.SPO2
}];

If you do not want to create a new object, you can use the following code snippet.
function orderKey(obj, keyOrder) {
keyOrder.forEach((k) => {
const v = obj[k]
delete obj[k]
obj[k] = v
})
}
here is a codepen: https://codepen.io/zhangyanwei/pen/QJeRxB

I think that's not possible in JavaScript.
You can create an array which will contain the field names in your order and you can iterate through this array and fetch the fields from the actual object.

Just refer to the object keys in the order that you like:
aKeys = [
addObjectResponse[0].DateTimeTaken,
addObjectResponse[0].Weight,
addObjectResponse[0].Height,
...etc...
]

I wrote a quick function in TypeScript that takes 2 arguments. The first is the array of objects you want to change the keys of, the second is an array of strings that represent the order of keys you'd like returned.
type GenericObject = Record<string, any> | null;
const order:Function = (data: Array<GenericObject>, order: Array<string>): Array<GenericObject> => {
return data.map((node) => {
return order.reduce((runningValue, currentValue) => {
return Object.assign(runningValue, { [currentValue]: node?.[currentValue]});
}, {});
});
};
And here is an example of calling it:
const data: Array<GenericObject> = [
{ b: 1, a: 2},
{ b: 3, a: 4},
];
const orderIWant: Array<string> = ['a', 'b'];
const ordered: Array<GenericObject> = order(data, orderIWant);
console.log(ordered);
// [ { a: 2, b: 1 }, { a: 4, b: 3 } ]

function orderKeys(obj, keys){
const newObj = {};
for(let key of keys){
newObj[key] = obj[key];
}
return newObj;
}