Find next available id in array of objects - javascript

I have an array of objects. These objects have a property id. I need a function which returns the next available id (which is not used by an object).
array = [
{
id: 1
},
{
id: 2
},
{
id: 5
},
{
id: 3
}
]
I would like to have a function which takes an array as an input and returns a number (which is the next free id).
In the example case:
findFreeId(array){
magic happens
}
result --> 4

How about something like this?
function findFreeId (array) {
const sortedArray = array
.slice() // Make a copy of the array.
.sort(function (a, b) {return a.id - b.id}); // Sort it.
let previousId = 0;
for (let element of sortedArray) {
if (element.id != (previousId + 1)) {
// Found a gap.
return previousId + 1;
}
previousId = element.id;
}
// Found no gaps.
return previousId + 1;
}
// Tests.
let withGap = [{id: 1}, {id: 2}, {id: 5}, {id: 3}];
let noGap = [{id: 1}, {id: 2}];
let empty = [];
console.log(findFreeId(withGap)); // 4
console.log(findFreeId(noGap)); // 3
console.log(findFreeId(empty)); // 1

A simple approach is to get all the ID values, sort them, then starting at 0 look for the first missing number in the sequence. That may be OK where efficiency doesn't matter, but a more efficient method is to:
Get the IDs
Sort them
Step through the values to get the next available number
Insert the value in the list of IDs
Store the value so next time it starts at #3 from the previous value + 1
E.g.
class IDStore {
constructor(dataArray) {
if (!Array.isArray(dataArray)) {
return null;
}
this.previousIndex = 0;
this.indexes = dataArray.map(obj => obj.id).sort();
}
get nextIndex() {
while (this.indexes[this.previousIndex] == this.previousIndex) {
this.previousIndex++;
}
return this.previousIndex;
}
addIndex(index) {
if (!Number.isInteger(index) || this.indexes.find[index]) {
return null;
}
this.indexes.push(index);
this.indexes.sort();
return index;
}
}
var data = [ { id: 1 }, { id: 2 }, { id: 5 }, { id: 3 } ];
// Create an ID store
var idStore = new IDStore(data);
// Insert more objects in the array with unique IDs
for (var i=0, next; i<4; i++) {
// Current list of indexes
console.log('Indexes: ' + idStore.indexes);
// Get the next available index
next = idStore.nextIndex;
console.log('Next available: ' + next);
// Calling nextIndex doesn't affect next index
next = idStore.nextIndex;
console.log('Next available: ' + next);
// Use next index
data.push({id: next});
// Adding next index is manual
idStore.addIndex(next);
console.log('Added: ' + next);
}
// Data structure is independent
console.log('End: ' + JSON.stringify(data));
This is somewhat simplistic in that it assumes the IDs are sequential integers starting at 0 and doesn't have much validation or error handling.
Maintaining the id is separate from adding new members to the data array. It would be much better to combine the operations, so an "add object" method gets the next available ID, adds it to the object, adds the object to the array, updates the index and returns the new ID.

const findFreeId = (ids) => {
let id = 0;
for (id; ; id++) {
let isFree = true;
for (let i = 0; i < array.length; i++) {
const e = ids[i];
if (e === id) {
isFree = false;
break;
}
}
if (isFree) break;
}
return id;
}

Related

I need help simplifying code that compares various properties of objects

I have a strong suspicion my code is way too clunky and can be written in a more concise and efficient manner. The intent is to compare an array of objects (representing players) to find the player with the highest majorityScore property. If there are more than one player sharing the same high score, then compare the co-winners' factions with a map (priorityMap) to determine who wins.
players = [
{
majorityScore: 4,
faction: 'AR'
},
{
majorityScore: 8,
faction: 'MOU'
},
{
majorityScore: 2,
faction: 'MOB'
},
{
majorityScore: 8,
faction: 'I'
}
];
const priorityMap = {
'MOB': 1,
'I': 2,
'MOU': 3,
'AR': 4,
'S' : 0
}
let winner;
let highScore = -1;
let duplicates = [];
for(let i = 0; i < players.length; i++){
if(players[i].majorityScore > highScore){
highScore = players[i].majorityScore;
winner = players[i]
duplicates = [winner];
} else if (players[i].majorityScore === highScore){
duplicates.push(players[i]);
};
}
if(duplicates.length > 1){
let highFactionScore = duplicates.reduce((a,v) => {
if(priorityMap[v.faction] > a){
a = priorityMap[v.faction];
}
return a;
}, 0);
let winningFaction = Object.keys(priorityMap).find((k) => {
return priorityMap[k] === highFactionScore;
});
winner = duplicates.filter((v) => {
return v.faction === winningFaction
})
}
Since you are reducing an array of objects into one object, the reduce function can be used here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
Instead of checking the factions after getting the players with the highest majority score, you can check the factions whenever you end up comparing players with the same majority score.
let winner = players.reduce((accum, currVal) => {
if (accum.majorityScore < currVal.majorityScore) {
return currVal;
} else if (accum.majorityScore > currVal.majorityScore) {
return accum;
} else {
return priorityMap[accum.faction] > priorityMap[currVal.faction] ? accum : currVal
}
});
Here's a slightly shorter method. It uses a temp object to maintain a dictionary where the scores are the keys. As we iterate we add the value of priorityMap[faction] to the score property, and change it only if the value is greater than the one stored.
const players=[{majorityScore:4,faction:"AR"},{majorityScore:8,faction:"MOU"},{majorityScore:8,faction:"MOU12"},{majorityScore:8,faction:"MOU20"},{majorityScore:2,faction:"MOB"},{majorityScore:2,faction:"MOB2"},{majorityScore:8,faction:"I"}],priorityMap={MOB:1,I:2,MOU:3,MOB2:4,AR:4,S:0,MOU12:21,MOU20:22};
function getGroups(arr) {
// Create the temp object
// We'll be using the scores as keys, and using
// the value in priorityMap as the value
// As we iterate we check the new priorityMap value
// against the old one
const temp = {};
// Iterate over the players array
return arr.reduce((acc, c) => {
const { majorityScore: score, faction } = c;
// If the accumulator object doesn't have a key that
// matches the score, add a new object
acc[score] = (acc[score] || { majorityScore: score, faction });
// If the new value of priorityMap[faction] is
// greater than the one stored in temp
// update the faction in the accumulator for that score
if (priorityMap[faction] > temp[score]) {
acc[score].faction = faction;
}
// Update the temp object with the
// priorityMap[faction] value
temp[score] = priorityMap[faction];
// Return the accumulator for the next iteration
return acc;
}, {});
}
console.log(getGroups(players));

Very simple increment function in objects list

I’m trying to replicate a very simple function that I can get to work with arrays but not with objects. I just want to be able to run a function that logs the next object number as with the numbers array.
Take this working array as an example:
var numbers = [4,2,6],
count = 0;
incrementArr();
function incrementArr() {
if (count < numbers.length) { // if not last array element
console.log(numbers[count]);
count++;
} else {
console.log(numbers[0]);
count = 1;
}
}
Whenever you run the incrementArr function, it’ll just log the next number and then return to the start if the current state (count) is at the end.
However, I cannot replicate the same principle with this object list:
var objs = {
first: { // doesn't have to have 'first'
"number": 4
},
second: { // doesn't have to have 'second'
"number": 2
},
third: { // doesn't have to have 'third'
"number": 6
}
},
count = 0;
incrementObj();
function incrementObj() {
if (count < Object.keys(objs).length) { // if not last obj element
//objs["first"].number
console.log(objs[count].number);
count++;
} else {
console.log(objs["first"].number); // what if no "first" in objects?
count++;
}
}
How could the incrementObj function work the same way that the previous incrementArr function works?
It seems that I can’t pick the specific object instance (e.g. numbers[1] from the array would pick the 2nd number, but only objs[“second”].number would pick the 2nd object, which isn’t iterable if you know what I mean). How could I get a workaround for typical circumstances like this?
So essentially, what’s the difference between this:
first: { // doesn't have to have 'first'
"number": 4
}
and:
{ // doesn't have to have 'first'
"number": 4
}
Why have the "first" etc? (called the key?)
Is there generally a better way of going about object lists (it's difficult to explain)? Thanks for any advice here.
You could take a closure over the object and get the keys and store an index. The returned function get the value and increment and adjusts the index.
function increment(object) {
var keys = Object.keys(object),
index = 0;
return function() {
var value = object[keys[index]].number;
index++;
index %= keys.length;
return value;
};
}
var objs = { first: { number: 4 }, second: { number: 2 }, third: { number: 6 } },
incrementObj = increment(objs);
console.log(incrementObj());
console.log(incrementObj());
console.log(incrementObj());
console.log(incrementObj());
Try this, it access keys through the array generated from keys, objects are unordered list that means you will have to at least order the keys and access them in the array order.
const keysArr = Object.keys(objs);
function incrementObj() {
if (count < keysArr.length) { // if not last obj element
//
console.log(objs[keysArr[count]].number);
count++;
} else {
console.log(objs["first"].number); // what if no "first" in objects?
count++;
}
}
I propose using iterators
See this codepen
If your object have specific shapes, then you use this as a lens to find the number property you want. I'm not sure how you want to use the iterator and have return both the key and the value as separate properties, but you can as well return { [keys[nextIndex]]: values[nextIndex] } or find other shape (the world is your oyster).
Provided you go this length, why not try use RxJs to make your object an observable?
var objs = {
first: { // doesn't have to have 'first'
"number": 4
},
second: { // doesn't have to have 'second'
"number": 2
},
third: { // doesn't have to have 'third'
"number": 6
}
}
function propertyIterator(obj) {
const keys = Object.keys(obj)
const values = Object.values(obj)
const length = keys.length
let nextIndex = 0
return {
next: function() {
const value = {
key: keys[nextIndex],
value: values[nextIndex]
}
let done = false
if (nextIndex >= length) {
done = true
}
nextIndex += 1
return { current: value, done: done}
}
}
}
const incrementObj = propertyIterator(objs)
let result = incrementObj.next()
console.log(result.current.key, result.current.value.number || NaN)
result = incrementObj.next()
console.log(result.current.key, result.current.value.number || NaN)
result = incrementObj.next()
console.log(result.current.key, result.current.value.number || NaN)
using generators, see this codepen:
const objs = {
first: { // doesn't have to have 'first'
"number": 4
},
second: { // doesn't have to have 'second'
"number": 2
},
third: { // doesn't have to have 'third'
"number": 6
}
}
const inc = defaultValue => prop => function* (obj) {
for(let key in obj) {
yield obj[key][prop] || defaultValue
}
}
const getNumber = inc(NaN)('number')
const it = getNumber(objs)
let result = it.next()
while (!result.done) {
console.log(result.value)
result = it.next()
}

array indexOf with objects?

I know we can match array values with indexOf in JavaScript. If it matches it wont return -1.
var test = [
1, 2, 3
]
// Returns 2
test.indexOf(3);
Is there a way to match objects? For example?
var test = [
{
name: 'Josh'
}
]
// Would ideally return 0, but of course it's -1.
test.indexOf({ name: 'Josh' });
Since the two objects are distinct (though perhaps equivalent), you can't use indexOf.
You can use findIndex with a callback, and handle the matching based on the properties you want. For instance, to match on all enumerable props:
var target = {name: 'Josh'};
var targetKeys = Object.keys(target);
var index = test.findIndex(function(entry) {
var keys = Object.keys(entry);
return keys.length == targetKeys.length && keys.every(function(key) {
return target.hasOwnProperty(key) && entry[key] === target[key];
});
});
Example:
var test = [
{
name: 'Josh'
}
];
var target = {name: 'Josh'};
var targetKeys = Object.keys(target);
var index = test.findIndex(function(entry) {
var keys = Object.keys(entry);
return keys.length == targetKeys.length && keys.every(function(key) {
return target.hasOwnProperty(key) && entry[key] === target[key];
});
});
console.log(index);
Note that findIndex was added in ES2015, but is fully polyfillable.
Nope, you can't and the explanation is simple. Despite you use the same object literal, two different objects are created. So test would have another reference for the mentioned object if you compare it with the reference you are looking for in indexOf.
This is kind of custom indexOf function. The code just iterates through the items in the object's array and finds the name property of each and then tests for the name you're looking for. Testing for 'Josh' returns 0 and testing for 'Kate' returns 1. Testing for 'Jim' returns -1.
var test = [
{
name: 'Josh'
},
{
name: 'Kate'
}
]
myIndexOf('Kate')
function myIndexOf(name) {
testName = name;
for (var i = 0; i < test.length; i++) {
if(test[i].hasOwnProperty('name')) {
if(test[i].name === testName) {
console.log('name: ' + test[i].name + ' index: ' + i);
return i;
}
}
}
return -1;
}
You can loop on array and then look for what you want
var test = [{ name: 'Josh' }]
const Myname = test.map((item) => { return item.name; }).indexOf("Josh")

Check if an object with index is in array

$.each(constructions, function(i,v) {
if ($.inArray(v.name, map[ii].buildings) == -1) {//stuff}
};
Where constructions is an array of objects, each with a unique name. map[ii].buildings is an array containing some of these objects. I want to iterate each object in constructions, checking if its name parameter appears in the objects of map[ii].buildings.
The above code works if the each element in the map[ii].buildings array is just the text string of the object name, but not if the element is the entire object.. close, but no dice >.<
Try using $.grep() instead of $.inArray(); you can specify a function to do the filtering for you.
Instead of checking for -1, you check whether the array that $.grep() returns has length == 0
Simple example: (would be easier if you posted the code / example of what "constructions" objects look like)
var constructions = [{
Name: "Mess hall",
SqFt: 5000
}, {
Name: "Infirmary",
SqFt: 2000
}, {
Name: "Bungalow",
SqFt: 2000
}, {
Name: "HQ",
SqFt: 2000
}];
var buildings = [{
Name: "Infirmary",
SqFt: 2000
}, {
Name: "HQ",
SqFt: 2000
}];
// found buildings will be list of items in "constructions" that is not in "buildings"
var foundBuildings = $.grep(constructions, function (constructionsItem) {
return $.grep(buildings, function (buildingsItem) {
return buildingsItem.Name === constructionsItem.Name
}).length == 0; // == 0 means "not in", and > 0 means "in"
});
// this just renders the results all pretty for ya
$.each(foundBuildings, function (idx, item) {
$("#output").append("<div>" + item.Name + "</div>");
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id='output'></div>
Example jsFiddle: http://jsfiddle.net/eLeuy9eg/3/
The non-jQuery way of doing this would be to use filter. Something like this:
// pass in an array and the key for which you want values
// it returns an array of those values
function getValues(arr, key) {
return arr.map(function (el) { return el[key]; });
}
function notFoundIn(arr, arr2) {
// grab the names of the buildings
var buildings = getValues(arr2, 'name');
// grab the names from the construction objects and filter
// those that are not in the building array
return getValues(arr, 'name').filter(function (el) {
return buildings.indexOf(el) === -1;
});
}
notFoundIn(constructions, buildings); // eg [ "one", "three" ]
DEMO
You could even add a new method to the array prototype. With this one you can use either simple arrays, or arrays of objects if you pass in a key. Note in this example I've replaced map and filter with loops that perform the same functions, but faster (see comments):
function getValues(arr, key) {
var out = [];
for (var i = 0, l = arr.length; i < l; i++) {
out.push(arr[i][key]);
}
return out;
}
if (!Array.prototype.notFoundIn) {
Array.prototype.notFoundIn = function (inThisArray, key) {
var thisArr = key ? getValues(this, key) : this;
var arrIn = key ? getValues(inThisArray, key) : inThisArray;
var out = [];
for (var i = 0, l = thisArr.length; i < l; i++) {
if (arrIn.indexOf(thisArr[i]) === -1) {
out.push(thisArr[i]);
}
}
return out;
}
}
constructions.notFoundIn(buildings, 'name');
[1, 2, 3].notFoundIn([2]); // [1, 3]
DEMO

JS .indexOf('string') returns -1

I have an Array[] this.unusedInstruments:
[
{ label: 'one'},
{ label: 'two'},
{ label: 'three'}
]
and a function: (params getting passed in are verified as being 'one', 'two', or 'three'
removeInstrument: function(removedIntrument) {
var index = this.unusedInstruments.indexOf(removedIntrument);
delete this.unusedInstruments[index];
},
but I am not getting what I expected. I logged the index, and it is always returning -1 despite the parameter. I am assuming that it is saying that the index doesn't exist, but I guess that means I don't know how to query the parent Array for the indexed Object.
As soon as it's an array - you cannot just delete its elements, otherwise you'll get a holes with undefined value. So you need a bit more intelligent way of doing that:
removeInstrument: function(removedInstrument) {
var len = this.unusedInstruments.length,
i;
var remove = function(arr, from) {
// Based on John Resig's article (MIT Licensed)
// http://ejohn.org/blog/javascript-array-remove/
var rest = arr.slice(from + 1);
arr.length = from;
return arr.push.apply(arr, rest);
};
for (i = 0; i < len ; ++i) {
if (this.unusedInstruments[i].label == removedInstrument) {
remove(this.unusedInstruments, i);
break;
}
}
}
remove() function implementation idea is borrowed at https://stackoverflow.com/a/9815010/251311
.indexOf() will only work if the string is an element of the array you're searching. But in your data, the string is the value of the label property of the element, it's not the element itself. You need to write a loop that drills into the objects and compares with the property.
removeInstrument: function(removedInstrument) {
for (i = 0; i < this.unusedInstruments.length; i++) {
if (this.unusedInstruments[i].label == removedInstrument) {
delete this.unusedInstruments[i];
break;
}
}
}

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