I am trying to find whether the value roomTypeFilter exists within an Object inside an array. I then want to perform conditional statements depending whether the value roomTypeFilter exists or not.
Below is my code
function includes(k) {
for (var i = 0; i < this.length; i++) {
if (this[i] === k || (this[i] !== this[i] && k !== k)) {
return true;
}
}
return false;
}
var dayValue = this.ui.dayConstraintList.val();
var arr = [courseTemplate.get('dayConstraints')[dayValue]];
console.log(arr);
arr.includes = includes;
console.log(arr.includes('roomTypeFilter'));
The first console.log returns an Object inside an array.
The second console.log returns false, in this case as roomTypeFilter exists inside the Object I want to return 'true' but I am unsure how to do so, any help would be greatly appreciated.
Instead of using includes, use hasOwnProperty. Take a look here for more information on the hasOwnProperty. It's pretty self-explanatory from its name - it essentially returns a boolean on whether or not the object has a property. I.e., in your case, you would use:
arr[0].hasOwnProperty('roomTypeFilter');
You can use hasOwnProperty method to check if object contains roomTypeFilter property.
...
if (this[i].hasOwnProperty(k)) {
...
}
...
You could refactor your includes function to use
array.prototype.some
some() executes the callback function once for each element present in the array until it finds one where callback returns a truthy value... If such an element is found, some() immediately returns true.
Here is an example.
var arr = [
{
roomTypeFilter: {
name: 'foo'
}
},
["roomTypeFilter", "foo"],
"roomTypeFilter foo"
]
function includes(arr, k) {
return arr.some(function(item) {
return item === Object(item) && item.hasOwnProperty(k);
})
}
console.log("Does arr includes roomTypeFilter ? - ", includes(arr, 'roomTypeFilter'))
Related
Don't know what to put before the for loop. Don't know if I need an if/else statement. Trying to have it display in the console if items in an array are strings. So I know I need consol.log
var stringOne = isString('rob','bob','carl')
function isString() {
//I dont know what to put before for loop
for(let i = 0; i < arguments.length; i++) {
// Dont know if i need an if/else statement
// Trying to have it display in the console if items in an array are strings
// So I know I need consol.log
}
}
every would be appropriate here, and doing I/O (like console.log) is better left outside of the function. The name of the function suggests that it should return a boolean (true/false):
function isString(...args) {
return args.every(s => typeof s === "string");
}
console.log(isString('rob','bob','carl'));
Because it seems like you're a beginner, I will expand upon the code that you currently have, although #trincot did the best solution.
In a for loop, you can return a value so the loop won't continue. Because you only need to check if any of them are false, may it be in position 0, 1 or 2 in the array, you can return "false" immediately.
If there are only strings, the loop will continue until it ends, and then return "true" at the end of the method.
So you don't need any code before the for loop, only an if statement that returns "false" if any of the items in the array isn't a string.
var stringOne = isString('rob','bob','carl')
var stringTwo = isString('rob','bob', 1)
function isString() {
for(let i = 0; i < arguments.length; i++) {
if (typeof arguments[i] != 'string') {
return false
}
}
return true
}
console.log({stringOne});
console.log({stringTwo});
Something like this in the loop ought to do it:
this_arg = arguments[i];
if (typeof this_arg === 'string') console.log("arg number " + i + " is a string");
It shows how to do it a bit here
You may find every useful here. It iterates over the array you've made from the arguments and checks to see if each element matches the condition. If they all match it returns true, otherwise false.
function isString() {
return Array.from(arguments).every(str => {
return typeof str === 'string';
});
}
console.log(isString('rob','bob','carl'));
console.log(isString(2,'bob','carl'));
I am trying to check if an object is already in an array, following this answer here: How to determine if object is in array
I adjusted the function to suit my needs, and now it looks like this:
var _createDatesArray, _objInArray;
_objInArray = function(array, obj) {
var i;
i = 0;
while (i < array.length) {
console.log("array[i] == obj is ", array[i] === obj, " array[i] is ", array[i], " and obj is ", obj);
if (array[i] === obj) {
return true;
}
i++;
}
};
_createDatesArray = function(val) {
var result;
if (val != null) {
result = {
text: val
};
if (!_objInArray(scope.datesQuestion.dates, result)) {
scope.datesQuestion.dates.push(result);
}
return console.log(scope.datesQuestion.dates);
}
};
What I need to do, is basically see if the object is already in the array, and if is,t return true.
When debugging, the result of the console log is the following:
array[i] == obj is false array[i] is {text: "10/08/17"} and obj is
{text: "10/08/17"}
and the function says they are different (array[i] == obj is false) but they look the same to me.
I also checked the type of both, which is this:
typeof array[i] is "object"
typeof obj is "object"
can you help me with this? Why are they different? what can be different?
_createDatesArray is called when $scope of my angular app changes its value based on a ng-model, but I don't think this is relevant
They're two different objects with the same content. Comparing them with == or === will yield false.
Since you're using AngularJS, you can use angular.equals() instead to perform a deep comparison of the object's properties.
The objects you are comparing don't have the same reference, so == is returning false. See Object comparison in JavaScript for a more detailed explanation.
In this particular case, you could simply compare the text of dates to see if they are equivilant. However this wouldn't work for all objects like the function name suggests.
if (arr[i].text === obj.text)
Alternatively, you could create a method specific for checking if your array includes a given date and simplify it greatly using Array.prototype.some:
dateInArray = function (array, date) {
return array.some(function (arrayDate) {
return arrayDate.text === date.text
})
}
Or, more succinctly using ES6 arrow functions:
dateInArray = (array, date) => array.some(arrayDate => arrayDate.text === date.text)
array[i] === obj will return true ONLY if its the same object. In the link that you have referred the object being checked is the same object that is inserted in the array, thats why it returns true. In your case, you are creating a new object 'result' and adding the value in there. So the array does not contain the exact same object and hence returns false.
If 'text' is the only property in the object, instead of checking for the entire object you could check if the 'text' property in both the objects is same.
_objInArray = function(array, obj) {
var i;
i = 0;
while (i < array.length) {
if (array[i].text === obj.text) {
return true;
}
i++;
}
};
This happens because objects in JS are compared by reference, but not by values they have. But you need to compare objects by their value. So you need to get some third-party function or to write your own. One more option is to use angular built-in equals function.
angular.equals($scope.user1, $scope.user2);
For a better understanding you can read a good article on this subject here.
The following function takes an object, loops through each value and returns false if the object or its children have an empty or undefined property web. Otherwise, it returns true:
hasNoCategories (object) {
for (let key in object) {
const value = object[key]
for (let i = 0; i < value.length; i++) {
const item = value[i]
if (item.web !== undefined && item.web !== '') return false
}
if (key === 'web' && value !== '') {
return false
}
}
return true
},
Example input:
{
"livingroom": [],
"garage": [],
"outdoors": [],
"other": [],
"id": "ZI4hteKxgr",
"name": "Cuiti",
"description": "",
"user": "",
"date": "2016/5/13",
}
How to rewrite this function without using for loops?
I'm not 100% sure what you expect the code to do, because your existing code and your description differ.
Your description is, rephrased, that this function checks whether object.web or any object.XXX.web are undefined. Your code however assumes that all members are arrays and checks whether object.web or object.XXX[YYY].web are undefined. (Note that it also doesn't do it correctly and accesses .length even though the member in question might be undefined.)
Since I'm not sure which of those is right, I'm providing two answers.
Functionality as per your textual description:
function hasNoCategories(object) {
if(!object.web) return false;
return Object.keys(object).every(function(key) {
if(typeof object[key] !== 'object') return true;
return !!object[key].web;
});
}
Functionality as per your existing code: (but with the length property access fixed)
function hasNoCategories(object) {
if(!object.web) return false;
return Object.keys(object).every(function(key) {
if(!Array.isArray(object[key])) return true;
return object[key].every(function(el) {
if(typeof object[key] !== 'object') return true;
return !!el.web;
});
});
}
To understand how this works, check out the documentation on Object.keys (which returns an array with the names of all keys in your object) and Array.prototype.every (which runs a callback function for every element in an array and returns true only if the callback returned true for every element).
Note that I'm assuming that your "empty or undefined" should reject all kinds of falsy values including null and the number (not string) zero. If not, then all the checks like if(!something) and return !!something would need to be changed to if(typeof something === "undefined" || something === '') and return typeof something !== "undefined" && something !== '', respectively.
Side note to prevent nitpicking: Of course there are still loops going on. But it was specifically asked "without for loop" and there is no for in this code.
I assume this is what you are looking for:
var hasNoCategories = function(object) {
if (!object.web) {
return false;
}
for (let key in object) {
var value = object[key];
if (!value.web) {
return false;
}
}
return true;
};
I got rid of 1 loop. But this cannot be done without loops because you have to loop over all children. You can hide this loop inside some another function but you cannot get rid of it.
If you really don't want to use loops (I don't know why), one of your options is to serialize the object and phrase the string for the word "web".
var s = JSON.stringify(object);
var webIndex = s.indexOf('web');
Now perform some checks around this index to ascertain if that has the value 'undefined' or ''. Please keep in mind that the word "web" can match as a part of another property name too. So, you need to include this possibility too to your checks.
I am trying to figure out if all of the elements in an array are keys in the object.
var obj = { name: 'Computer', cost: '$1,000' };
var myArray = [ 'name', 'cost', 'bio' ]; //another example would be var myArray = [];
for(var x = 0; x < myArray.length; x++){
if (myArray[x] in obj)
{
return true;
}
}
How can I check if all of the elements in an array are keys in the object?
Do it the other way around. If you find someone in the array who is NOT in the object then you return false. If you reach the end of the loop then you return true because all the keys were in the object.
Depending on what you want, this might do the trick:
function hasKeys(obj, keys) {
for (var i=0; i != keys.length; ++i) {
if (!(keys[i] in obj))
return false;
}
return true;
};
One subtlety you need to ask yourself: do you want to know if the object has the keys directly (i.e. not somewhere in its prototype stack?) If so, then replace keys[i] in obj with obj.hasOwnProperty(keys[i])
function hasKeys(obj, keys) {
return keys.every(Object.prototype.hasOwnProperty.bind(obj));
}
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every states, "The every method executes the provided callback function once for each element present in the array until it finds one where callback returns a falsy value (a value that becomes false when converted to a Boolean). If such an element is found, the every method immediately returns false. Otherwise, if callback returned a true value for all elements, every will return true. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values" (emphasis mine).
Array.some() makes for a clean solution.
// object in question
var obj = { ... };
// keys that need to be present in the object
var keys = [ ... ];
// iterate through the whitelist until we find a key that doesn't exist in the object. If all exist, that means Array.some() is false.
var valid = !keys.some(function(key) {
return !obj.hasOwnProperty(key);
});
An alternative solution would be using a similar concept, but with Array.every(). It is to note that this will generally be slower because it always has to touch every element in the whitelist.
// iterate through the whitelist, making sure the object has each key.
var valid = keys.every(obj.hasOwnProperty);
This problem can be expressed in terms of set inclusion: does the set of property keys completely include the array of required keys? So we can write it as
includes(Object.keys(obj), arr)
So now we just need to write includes.
function includes(arr1, arr2) {
return arr2.every(function(key) {
return contains(arr1, key);
}
}
For contains, we could use Underscore's _.contains, or just write it ourselves:
function contains(arr, val) {
return arr.indexOf(val) !== -1;
}
If we are interested in conciseness at the possible expense of readability, we could shorten our definition of includes to use Function#bind instead of the anonymous function:
function includes(arr1, arr2) {
return arr2.every(contains.bind(0, arr1));
}
Now we have functions we can use for other things, instead of mixing up the two different aspects of the problem--the keys of an object, and set inclusion. If we really want to write an all-in-one function, it becomes the somewhat more readable:
function hasMany(obj, arr) {
return arr.every(_.contains.bind(0, Object.keys(obj));
}
If we want more readability, like we were writing a novel:
function object_has_required_keys(object, required_keys) {
var object_keys = Object.keys(object);
function key_is_present(key) {
return object_keys.indexOf(key) !== -1;
}
return required_keys.every(key_is_present);
}
Underscore's _.intersection
If we're lazy (or smart), we could use Underscore's _.intersection to implement includes:
function includes(arr1, arr2) {
return _.intersection(arr1, arr2).length === arr2.length;
}
The idea is to take the intersection, and if the first array includes the second entirely, then the intersection will contain all the elements of the second array, which we can check by comparing their lengths.
Using ES6 sets
Thinking ahead to ES6, we could implement include using its sets, which ought to be faster:
function includes(arr1, arr2) {
var set = new Set(arr1);
return arr2.every(Set.prototype.has.bind(set));
}
Possible Duplicate:
Easiest way to find duplicate values in a javascript array
How do I check if an array has duplicate values?
If some elements in the array are the same, then return true. Otherwise, return false.
['hello','goodbye','hey'] //return false because no duplicates exist
['hello','goodbye','hello'] // return true because duplicates exist
Notice I don't care about finding the duplication, only want Boolean result whether arrays contains duplications.
If you have an ES2015 environment (as of this writing: io.js, IE11, Chrome, Firefox, WebKit nightly), then the following will work, and will be fast (viz. O(n)):
function hasDuplicates(array) {
return (new Set(array)).size !== array.length;
}
If you only need string values in the array, the following will work:
function hasDuplicates(array) {
var valuesSoFar = Object.create(null);
for (var i = 0; i < array.length; ++i) {
var value = array[i];
if (value in valuesSoFar) {
return true;
}
valuesSoFar[value] = true;
}
return false;
}
We use a "hash table" valuesSoFar whose keys are the values we've seen in the array so far. We do a lookup using in to see if that value has been spotted already; if so, we bail out of the loop and return true.
If you need a function that works for more than just string values, the following will work, but isn't as performant; it's O(n2) instead of O(n).
function hasDuplicates(array) {
var valuesSoFar = [];
for (var i = 0; i < array.length; ++i) {
var value = array[i];
if (valuesSoFar.indexOf(value) !== -1) {
return true;
}
valuesSoFar.push(value);
}
return false;
}
The difference is simply that we use an array instead of a hash table for valuesSoFar, since JavaScript "hash tables" (i.e. objects) only have string keys. This means we lose the O(1) lookup time of in, instead getting an O(n) lookup time of indexOf.
You could use SET to remove duplicates and compare, If you copy the array into a set it will remove any duplicates. Then simply compare the length of the array to the size of the set.
function hasDuplicates(a) {
const noDups = new Set(a);
return a.length !== noDups.size;
}
One line solutions with ES6
const arr1 = ['hello','goodbye','hey']
const arr2 = ['hello','goodbye','hello']
const hasDuplicates = (arr) => arr.length !== new Set(arr).size;
console.log(hasDuplicates(arr1)) //return false because no duplicates exist
console.log(hasDuplicates(arr2)) //return true because duplicates exist
const s1 = ['hello','goodbye','hey'].some((e, i, arr) => arr.indexOf(e) !== i)
const s2 = ['hello','goodbye','hello'].some((e, i, arr) => arr.indexOf(e) !== i);
console.log(s1) //return false because no duplicates exist
console.log(s2) //return true because duplicates exist
Another approach (also for object/array elements within the array1) could be2:
function chkDuplicates(arr,justCheck){
var len = arr.length, tmp = {}, arrtmp = arr.slice(), dupes = [];
arrtmp.sort();
while(len--){
var val = arrtmp[len];
if (/nul|nan|infini/i.test(String(val))){
val = String(val);
}
if (tmp[JSON.stringify(val)]){
if (justCheck) {return true;}
dupes.push(val);
}
tmp[JSON.stringify(val)] = true;
}
return justCheck ? false : dupes.length ? dupes : null;
}
//usages
chkDuplicates([1,2,3,4,5],true); //=> false
chkDuplicates([1,2,3,4,5,9,10,5,1,2],true); //=> true
chkDuplicates([{a:1,b:2},1,2,3,4,{a:1,b:2},[1,2,3]],true); //=> true
chkDuplicates([null,1,2,3,4,{a:1,b:2},NaN],true); //=> false
chkDuplicates([1,2,3,4,5,1,2]); //=> [1,2]
chkDuplicates([1,2,3,4,5]); //=> null
See also...
1 needs a browser that supports JSON, or a JSON library if not.
2 edit: function can now be used for simple check or to return an array of duplicate values
You can take benefit of indexOf and lastIndexOf. if both indexes are not same, you have duplicate.
function containsDuplicates(a) {
for (let i = 0; i < a.length; i++) {
if (a.indexOf(a[i]) !== a.lastIndexOf(a[i])) {
return true
}
}
return false
}
If you are dealing with simple values, you can use array.some() and indexOf()
for example let's say vals is ["b", "a", "a", "c"]
const allUnique = !vals.some((v, i) => vals.indexOf(v) < i);
some() will return true if any expression returns true. Here we'll iterate values (from the index 0) and call the indexOf() that will return the index of the first occurrence of given item (or -1 if not in the array). If its id is smaller that the current one, there must be at least one same value before it. thus iteration 3 will return true as "a" (at index 2) is first found at index 1.
is just simple, you can use the Array.prototype.every function
function isUnique(arr) {
const isAllUniqueItems = input.every((value, index, arr) => {
return arr.indexOf(value) === index; //check if any duplicate value is in other index
});
return isAllUniqueItems;
}
One nice thing about solutions that use Set is O(1) performance on looking up existing items in a list, rather than having to loop back over it.
One nice thing about solutions that use Some is short-circuiting when the duplicate is found early, so you don't have to continue evaluating the rest of the array when the condition is already met.
One solution that combines both is to incrementally build a set, early terminate if the current element exists in the set, otherwise add it and move on to the next element.
const hasDuplicates = (arr) => {
let set = new Set()
return arr.some(el => {
if (set.has(el)) return true
set.add(el)
})
}
hasDuplicates(["a","b","b"]) // true
hasDuplicates(["a","b","c"]) // false
According to JSBench.me, should preform pretty well for the varried use cases. The set size approach is fastest with no dupes, and checking some + indexOf is fatest with a very early dupe, but this solution performs well in both scenarios, making it a good all-around implementation.
function hasAllUniqueChars( s ){
for(let c=0; c<s.length; c++){
for(let d=c+1; d<s.length; d++){
if((s[c]==s[d])){
return false;
}
}
}
return true;
}