The story is, I should be able to put Bob, Sally and Jack into a box. I can also remove either from the box. When removed, no slot is left.
people = ["Bob", "Sally", "Jack"]
I now need to remove, say, "Bob". The new array would be:
["Sally", "Jack"]
Here is my react component:
...
getInitialState: function() {
return{
people: [],
}
},
selectPeople(e){
this.setState({people: this.state.people.concat([e.target.value])})
},
removePeople(e){
var array = this.state.people;
var index = array.indexOf(e.target.value); // Let's say it's Bob.
delete array[index];
},
...
Here I show you a minimal code as there is more to it (onClick etc). The key part is to delete, remove, destroy "Bob" from the array but removePeople() is not working when called. Any ideas? I was looking at this but I might be doing something wrong since I'm using React.
When using React, you should never mutate the state directly. If an object (or Array, which is an object too) is changed, you should create a new copy.
Others have suggested using Array.prototype.splice(), but that method mutates the Array, so it's better not to use splice() with React.
Easiest to use Array.prototype.filter() to create a new array:
removePeople(e) {
this.setState({people: this.state.people.filter(function(person) {
return person !== e.target.value
})});
}
To remove an element from an array, just do:
array.splice(index, 1);
In your case:
removePeople(e) {
var array = [...this.state.people]; // make a separate copy of the array
var index = array.indexOf(e.target.value)
if (index !== -1) {
array.splice(index, 1);
this.setState({people: array});
}
},
Here is a minor variation on Aleksandr Petrov's response using ES6
removePeople(e) {
let filteredArray = this.state.people.filter(item => item !== e.target.value)
this.setState({people: filteredArray});
}
Simple solution using slice without mutating the state
const [items, setItems] = useState(data);
const removeItem = (index) => {
setItems([
...items.slice(0, index),
...items.slice(index + 1)
]);
}
Use .splice to remove item from array. Using delete, indexes of the array will not be altered but the value of specific index will be undefined
The splice() method changes the content of an array by removing existing elements and/or adding new elements.
Syntax: array.splice(start, deleteCount[, item1[, item2[, ...]]])
var people = ["Bob", "Sally", "Jack"]
var toRemove = 'Bob';
var index = people.indexOf(toRemove);
if (index > -1) { //Make sure item is present in the array, without if condition, -n indexes will be considered from the end of the array.
people.splice(index, 1);
}
console.log(people);
Edit:
As pointed out by justin-grant, As a rule of thumb, Never mutate this.state directly, as calling setState() afterward may replace the mutation you made. Treat this.state as if it were immutable.
The alternative is, create copies of the objects in this.state and manipulate the copies, assigning them back using setState(). Array#map, Array#filter etc. could be used.
this.setState({people: this.state.people.filter(item => item !== e.target.value);});
Easy Way To Delete Item From state array in react:
when any data delete from database and update list without API calling that time you pass deleted id to this function and this function remove deleted recored from list
export default class PostList extends Component {
this.state = {
postList: [
{
id: 1,
name: 'All Items',
}, {
id: 2,
name: 'In Stock Items',
}
],
}
remove_post_on_list = (deletePostId) => {
this.setState({
postList: this.state.postList.filter(item => item.post_id != deletePostId)
})
}
}
filter method is the best way to modify the array without touching the state.
It returns a new array based on the condition.
In your case filter check the condition person.id !== id and create a new array excluding the item based on condition.
const [people, setPeople] = useState(data);
const handleRemove = (id) => {
const newPeople = people.filter((person) => person.id !== id);
setPeople( newPeople);
};
<button onClick={() => handleRemove(id)}>Remove</button>
Not advisable:
But you can also use an item index for the condition if you don't have any id.
index !== itemIndex
This is your current state variable:
const [animals, setAnimals] = useState(["dogs", "cats", ...])
Call this function and pass the item you would like to remove.
removeItem("dogs")
const removeItem = (item) => {
setAnimals((prevState) =>
prevState.filter((prevItem) => prevItem !== item)
);
};
your state variable now becomes:
["cats", ...]
Another way of doing it is by using useState hook. Check docs: https://reactjs.org/docs/hooks-reference.html#functional-updates It states: Unlike the setState method found in class components, useState does not automatically merge update objects. You can replicate this behavior by combining the function updater form with object spread syntax as shown below or use useReducer hook.
const [state, setState] = useState({});
setState(prevState => {
return {...prevState, ...updatedValues};
});
Some answers mentioned using 'splice', which did as Chance Smith said mutated the array. I would suggest you to use the Method call 'slice'
(Document for 'slice' is here) which make a copy of the original array.
Just filter out deleted item and update the state with remaining items again,
let remainingItems = allItems.filter((item) => {return item.id !== item_id});
setItems(remainingItems);
const [people, setPeople] = useState(data);
const handleRemove = (id) => {
const newPeople = people.filter((person) => { person.id !== id;
setPeople( newPeople );
});
};
<button onClick={() => handleRemove(id)}>Remove</button>
It's Very Simple
First You Define a value
state = {
checked_Array: []
}
Now,
fun(index) {
var checked = this.state.checked_Array;
var values = checked.indexOf(index)
checked.splice(values, 1);
this.setState({checked_Array: checked});
console.log(this.state.checked_Array)
}
removePeople(e){
var array = this.state.people;
var index = array.indexOf(e.target.value); // Let's say it's Bob.
array.splice(index,1);
}
Redfer doc for more info
Almost all the answers here seem to be for class components, here's a code that worked for me in a functional component.
const [arr,setArr]=useState([]);
const removeElement=(id)=>{
var index = arr.indexOf(id)
if(index!==-1){
setArr(oldArray=>oldArray.splice(index, 1));
}
}
If you use:
const[myArr, setMyArr] = useState([]);
for add:
setMyArr([...myArr, value]);
and for remove:
let index = myArr.indexOf(value);
if(index !== -1)
setPatch([...myArr.slice(0, index), ...myArr.slice(index, myArr.length-1)]);
Removing an element with a certain value
//
Note filter function always returns a new array.
const people = ["Bob", "Sally", "Jack"]
const removeEntry = (remove) => {
const upDatePeople = people.filter((Person) =>{
return Person !== remove
});
console.log(upDatePeople)
//Output: [ 'Sally', 'Jack' ]
}
removeEntry("Bob");
You forgot to use setState. Example:
removePeople(e){
var array = this.state.people;
var index = array.indexOf(e.target.value); // Let's say it's Bob.
delete array[index];
this.setState({
people: array
})
},
But it's better to use filter because it does not mutate array.
Example:
removePeople(e){
var array = this.state.people.filter(function(item) {
return item !== e.target.value
});
this.setState({
people: array
})
},
const [randomNumbers, setRandomNumbers] = useState([111,432,321]);
const numberToBeDeleted = 432;
// Filter (preferred)
let newRandomNumbers = randomNumbers.filter(number => number !== numberToBeDeleted)
setRandomNumbers(newRandomNumbers);
//Splice (alternative)
let indexOfNumberToBeDeleted = randomNumbers.indexOf(numberToBeDeleted);
let newRandomNumbers = Array.from(randomNumbers);
newRandomNumbers.splice(indexOfNumberToBeDeleted, 1);
setRandomNumbers(newRandomNumbers);
//Slice (not preferred - code complexity)
let indexOfNumberToBeDeleted = randomNumbers.indexOf(numberToBeDeleted);
let deletedNumber = randomNumbers.slice(indexOfNumberToBeDeleted, indexOfNumberToBeDeleted+1);
let newRandomNumbers = [];
for(let number of randomNumbers) {
if(deletedNumber[0] !== number)
newRandomNumbers.push(number);
};
setRandomNumbers(newRandomNumbers);
I got a problem with this Function. When I trigger this function it only re render the component the first trigger. After that not any more. I cant find the problem :(
function selectAnswer(id, questId) {
let newArr = questions
for(let i = 0; i < newArr.length; i++){
if(questId === newArr[i].id){
const changedAnswers = newArr[i].answers.map(answer => {
return answer.id === id ?
{...answer, selected: !answer.selected} :
{...answer, selected: false}
})
newArr.forEach(element => {
if(questId === element.id){
element.answers = changedAnswers
}
})
}
}
setQuestions(newArr)
}
You're never actually updating the state. This doesn't create a copy of the array, it just duplicates a reference to the array:
let newArr = questions
So this isn't setting state to a new array, but just a reference to the same array:
setQuestions(newArr)
Additionally, instead of creating new state, you are mutating the existing state:
element.answers = changedAnswers
Start by creating a new array, even if it contains the same elements as the original:
let newArr = [...questions];
Then, when you want to modify one of those elements, instead of modifying the existing element you would instead replace it with a new one. So instead of this structure:
newArr.forEach(element => {
});
You could instead replace your new array with a .map() over itself:
newArr = newArr.map(element => {
});
And within that .map() you would return either the unmodified object or the replacement object:
newArr = newArr.map(element => {
if(questId === element.id) {
return {...element, answers: changedAnswers};
} else {
return element;
}
});
Overall, the idea here is that you don't want to loop over an existing array, modify its values, and set that array back to state. That's not "updating state" in the React sense but instead it's "mutating state". Instead, create a new array and populate it with the objects you want. Those objects can be a mix of unchanged objects from the existing array and replaced (not modified) objects from the existing array.
{
"lion":{
"age_in_years":"10",
"name":"king",
"country":"africa"
},
"elephant":{
"age_in_years":"15",
"name":"hero",
"country":"usa"
},
"racoon":{
"age_in_years":"5",
"name":"thanos",
"country":"syria"
},
}
This is the data I'm getting through a web socket in react-native. I want to sort it in ascending order based on the "age_in_years". So the oldest animal's data should be shown at top and the youngest data at the last.
You sould better work with an array insted of object as below, first map it into array and parse the age_in_years and sort it.
const obj2Array = Object.entries(<YourObject>).map(([key, value]) => ({...value, _id: key, age_in_years: parseInt(value.age_in_years)}));
const sorted = obj2Array.sort((a, b) => a.age_in_years - b.age_in_years);
Then you can use .reduce if you want the object back, nevertheless you can use the sorted array to render it.
Sort by age in years oldest first
// use slice() to copy the array
var byAge = array.slice(0);
byAge.sort(function(a,b) {
return a.age_in_years - b.age_in_years ;
});
Store the values in array and make a sort function.
const numbers = [info.lion.age_in_years, info.elephant.age_in_years, info.racoon.age_in_years];
const ascNumbers = numbers.sort((a,b) => a-b);
If you need descending make it like this:
const descNumbers = numbers.sort((a,b) => b-a);
I am creating a dropdown filter to update the search results of a page using react hooks. Basically, I am passing an array with the options that the user chose from the dropdown menu. I am successfully updating the global state with the new arrays BUT my issue is useState creates a NEW array instead of merging the results with the previous state.
Above you can see, I made two calls with different filter options and the global state now holds 2 arrays. My goal is to have both arrays merged into one.
This is the function where the global state is being updated.
const Results = () => {
const [filterList, setFilterList] = useState([])
const setGlobalFilter = (newFilter) => {
let indexFilter = filterList.indexOf(newFilter);
// console.log("Top level index", indexFilter)
indexFilter ?
setFilterList([...new Set([...filterList, newFilter])]) :
setFilterList(filterList => filterList.filter((filter, i) => i !== indexFilter))
}
// console.log("TopFilterSelection:", filterList)
return (
<div>
<Filter setFilter={(filterList) => setGlobalFilter(filterList)}/>
</div>
)
}
I've been checking on using prevState like this:
...
setFilterList(prevState => [...new Set([...prevState, newFilter])]) :
...
But I don't know what I am doing wrong.
Any feedback would be much appreciated!
This happens because newFilteris an array, not a word.
Should be
setFilterList(previous => [...new Set([...previous, ...newFilter])])
Also this
let indexFilter = filterList.indexOf(newFilter);
always returns -1 if newFilteris an array (since you a sending brand new array each time), it's not a falsy value, be careful
Use the .concat method.
setFilterList(filterList.concat(newFilter))
Read more about it here:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat
I am trying to merge two array objects by the user_id key. The two array objects I get are from the state.
function mapStateToProps(state) {
let {users} = state.users.result;
let {invite} = state.invite.result;
let {friends} = state.friends.result;
if (users && invite && friends) {
let UsersList = mergeArray(users, invite.sent_invites); // Merge Users & Sent Invites
}
function mergeArray(a, b) {
return _.map(a, function(item) {
return _.assign(item, _.find(b, ['user_id', item.user_id]));
});
}
However, my {users} state also changes with the merge. Why is this? I have been stuck on this hours.
_.assign({}, item, _.find(b, ['user_id', item.user_id]));
_.assign assigns to the first argument, which in your cast was item, which was a reference to the object in state.users. So you make your first argument an empty object, so you are writing to a new object each time and won't modify any existing ones.