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Hi I want to delete key in array
here is my array
const data = [ { id: "2" } , { id: "4" } ]
I want ouput
['2','4']
here is what i try
data.map(function(item) {
//I return only item.id but output still not change
return item.id
})
That's because .map() method returns a new array, it does not alternate the current array. You need to store the returned array in another variable to get the required output like:
const data = [ { id: "2" } , { id: "4" } ]
const res = data.map(x => x.id)
console.log( res )
Or, using same variable:
let data = [ { id: "2" } , { id: "4" } ]
data = data.map(x => x.id)
console.log( data )
Map returns new array and do not alter source array. so you need to assign the result to a new variable.
const data = [{
id: "2"
}, {
id: "4"
}];
const output = data.map(function(item) {
return item.id
})
console.log(output)
Something like this? We map the key to a number and return it.
const data = [ { id: "2" } , { id: "4" } ];
var result = Object.keys(data).map(function (key) {
return Number(key);
});
console.log(result);
Related
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So basically I have an array of ids and I want to return only a simple array which I want to look like this
*[1,2,3]*
instead of
*[0:[1] , 1:[2]]*
Is there any way to do it
Code
const usersWhoHavePurchasedYourCourses = usersWhoHaveTokens.filter(
(user1: any) => {
return user1.tokens
?.map((token: any) => parseInt(token.course_id))
.includes(user.courses?.map((course: any) => course.id));
});
The output looks like this
output
As I said I don`t want to return this kind of output.
Edit
In attempting to reverse-engineer your logic, wouldn't you want to filter by checking if a user has at least one course? I recommend using Array.prototype.some as your filter result.
const user = { courses: [{ id: 1 }, { id: 2 }] };
const usersWhoHaveTokens = [
{ id: 1, tokens: [{ course_id: '1' }] },
{ id: 2, tokens: [{ course_id: '2' }] },
{ id: 3, tokens: [{ course_id: '3' }] },
];
// Compute the set, for faster processing
const userCourseIds = new Set(user.courses.map((course) => course.id));
const usersWhoHavePurchasedYourCourses = usersWhoHaveTokens
.filter(({ tokens }) => tokens
.some((token) => userCourseIds.has(parseInt(token.course_id))))
.map(({ id }) => id);
console.log(usersWhoHavePurchasedYourCourses); // [1, 2]
Original response
If you object is an 'object' type, you will need to transform it into an array, and then flatten it.
const
obj = { 0: [1], 1: [2] },
arr = Object.values(obj).flat();
console.log(JSON.stringify(arr)); // [1, 2]
If you want to preserve indices:
const
obj = { 1: [2], 5: [6] },
arr = Object.entries(obj).reduce((acc, [index, value]) => {
acc[+index] = value;
return acc;
}, []).map(([value]) => value);
console.log(JSON.stringify(arr)); // [null, 2, null, null, null, 6]
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i have this array
const names = [
{ name: 'Anna' },
{ num: 27 },
{ name: 'Valeria', age: 20},
{ secondname: 'Wilson' },
{ age: 12, name: 'Max' },
{ weight:'50kg', height: '172cm', name: 'Nick' }
]
using reduce i need to create new array that contains all names from initial array
i made like this, but i think it is bad
let allNames = names.reduce((previousValue, names) =>{
return previousValue + names.name},[])
console.log(allNames)
i did
allName.push(ar.name);
return allName;
}, []);
console.log(names);```
Array.reduce()
You have multiple options. You can use Array.reduce to merge them all into one array. You just need to check if name is defined.
names.reduce((allNames, person) => {
if (person.name) {
return [...allNames, person.name];
}
return allNames;
}, []);
Array.forEach()
Same for Array.forEach:
const allNames = [];
names.forEach((person) => {
if (person.name) {
allNames.push(person.name);
}
});
allNames;
Instead, I would recommend using Array.filter to remove all people without a name and map (Array.map) over them, to just return the names.
In terms of runtime, this would require you to loop twice over the array, but I think this is way more readable
Array.filter / Array.map
names
.filter((person) => person.name)
.map((person) => person.name);
Using reduce by including a check for objects that don't have the name property and an empty array as initial value:
const names = [
{ name: 'Anna' },
{ num: 27 },
{ name: 'Valeria', age: 20},
{ secondname: 'Wilson' },
{ age: 12, name: 'Max' },
{ weight:'50kg', height: '172cm', name: 'Nick' }
]
const reduceResult = names.reduce((previous, current) => {
if(current.name)
{
previous.push(current.name);
}
return previous;
}
,
[]);
console.log(reduceResult);
/*
[
"Anna",
"Valeria",
"Max",
"Nick"
]
*/
Using map, you will have undefined for objects that don't have a name property:
const mapResult = names.map(x => x.name);
console.log(mapResult);
/*
[
"Anna",
undefined,
"Valeria",
undefined,
"Max",
"Nick"
]
*/
filter + map can also be used but performance talking reduce is a better choice.
const filterMapResult = names.filter(({name}) => !!name).map(x => x.name);
console.log(filterMapResult);
/*
[
"Anna",
"Valeria",
"Max",
"Nick"
]
*/
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I need to assign the values of the below array of objects into defined variables which are initialized as empty strings.
What I have tried up until now:
const transaction = [{
number: 10,
value: "Ten"
},
{
number: 20,
value: "Twenty"
},
];
let transactionOneValue, transactionTwoValue, transactionOneNumber, transactionTwoNumber = "";
if (transaction.length > 0) {
transaction.forEach(item => {
[transactionOneNumber, transactionTwoNumber].forEach(num => num = item.number);
[transactionOneValue, transactionTwoValue].forEach(val => val = item.value);
});
}
Expected output:
transactionOneValue = "Ten",
transactionTwoValue = "Twenty",
transactionOneNumber = 10,
transactionTwoNumber = 20
How can I do it?
Destructuring seems to be simplest approach here, but I don't see how this would be useful. Creating separate variables for every item in a list isn't scalable.
let [
{number: transactionOneNumber, value: transactionOneValue},
{number: transactionTwoNumber, value: transactionTwoValue}
] = transaction
const transaction = [{
number: 10,
value: "Ten"
},
{
number: 20,
value: "Twenty"
},
];
let transactions = [];
if (transaction.length > 0) {
transaction.map((value, index, array) => {
for(x of Object.values(value)) {
transactions.push(x);
}
})
}
let transactionOneNumber = transactions[0],
transactionOneValue = transactions[1],
transactionTwoNumber = transactions[2],
transactionTwoValue = transactions[3];
console.log(transactionOneNumber);
console.log(transactionOneValue);
console.log(transactionTwoNumber);
console.log(transactionTwoValue);
output:
10
"Ten"
20
"Twenty"
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/values
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I have an object like this
{ '2020-08': {Invoice: 21400, Receipt: 20800, ...},
'2020-09': {Invoice: 8003.6, ...},
'2020-10': {Receipt: 7779.2, ...},
'2020-11': {Invoice: 32970, ...}
}
Wanna make it to be 2d array like this
[ ['2020-08', '2020-09', '2020-10', '2020-11'],
[ 21400 , 8003.6 , 0 , 32970 ], //Invoice
[ 20800 , 0 , 7779.2 , 0 ], //Receipt
...
]
It is very easy to achieve using Object.keys.
const data = {
'2020-08': {
Invoice: 21400,
Receipt: 20800
},
'2020-09': {
Invoice: 8003.6,
Receipt: 7779
},
'2020-10': {
Receipt: 7779.2,
Invoice: 32970
},
'2020-11': {
Invoice: 32970,
}
}
const res = []
const keys = [...Object.keys(data)]
const d = Object.keys(data).map(item => {
return data[item]["Invoice"] || 0
})
const d1 = Object.keys(data).map(item => {
return data[item]["Receipt"] || 0
})
console.log([keys, d, d1])
Try:
let result = [], key= [], invoice= [], receipt = [];
Object.keys(obj).forEach((x) => {
key.push(x);
invoice.push(obj[x].Invoice || 0);
receipt.push(obj[x].Receipt || 0);
});
result = [key,invoice,receipt];
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I'm trying to convert the array to map,
The array looks like :
var array = [{
"id" : 123
}, {
"id" : 456
}, {
"id" : 789
}];
The final object I'm trying to build should look like :
var result = {
"123": { id: 123 } ,
"456": { id: 456 } ,
"789": { id: 789 }
};
Any efficient way to implement it will be appreciated :)
Thanks
var array = [
{
"id": 123,
"otherProp": "true"
},
{
"id": 456,
"otherProp": "false"
},
{
"id": 789,
"otherProp": "true"
}
];
var result = array.reduce(function (acc, cur, i) {
acc[cur.id] = cur;
return acc;
}, {});
console.log(result);
Use javaScript reduce
The reduce() method applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
Use reduce
var array = [{
"id" : 123
}, {
"id" : 456
}, {
"id" : 789
}];
var expectedValue = {
"123": { id: 123 } ,
"456": { id: 456 } ,
"789": { id: 789 }
};
var result = array.reduce( (acc, c) => (acc[ c.id ] = c, acc) ,{});
console.log('result : ', result);
console.log('(JSON.stringify(expectedValue) === JSON.stringify(result)) ? ', (JSON.stringify(expectedValue) === JSON.stringify(result)));
.as-console-wrapper { max-height: 100%!important; top: 0; }
Explanation
Use reduce to iterate and initialize the accumulator to {}
Set the key as id of item of every iteration c and value as c itself.