I have an array [1, 2, 3] and I want to transfer it to object with nested parent-child objects's series like this :
{ value: 1, rest: { value: 2, rest: { value: 3, rest: null } }
If I have an array [1, 2, 3, 4] the result will be like this :
{ value: 1, rest: { value: 2, rest: { value: 3, rest: { value:4, rest:null } }
The best effort of me is this snippet of code :
const arrayToList = (array) => {
let list = { value: null, rest: null };
for (let e of array) {
array.indexOf(e) === 0 && (list.value = e);
array.indexOf(e) >= 1 && (list.rest = { value: e });
}
return list;
};
console.log(arrayToList([1, 2, 3]));
You can use reduceRight like so:
let obj = arr.reduceRight((rest, value) => ({ value, rest }), null);
It starts building the object from the inside out; it starts by creating the innermost object and then it uses that object as the rest property for the next outer object and so on until there are no more items in the array.
Demo:
let obj = [1, 2, 3, 4].reduceRight((rest, value) => ({ value, rest }), null);
console.log(obj);
You can create such object by running below recursive function:
let arr = [1, 2, 3, 4];
let transform = (arr, obj) => {
if(arr.length === 0){
return obj;
} else {
let last = arr[arr.length - 1];
let newArr = arr.slice(0, arr.length - 1);
return transform(newArr, { value: last, rest: obj || null })
}
};
console.log(transform(arr));
Use a recursive function:
let array = [1, 2, 3];
function arrayToL(array) {
let el = array.splice(0, 1)[0];
let rtn = {
value: el
}
rtn.rest = (array.length > 0) ? arrayToL(array) : null;
return rtn;
}
console.log(arrayToL(array));
I suggest another solution using the spread operator and reversing the array and start building object from the array end :
let arr = [1, 2, 4, 5]
let obj = {} //object to be built
arr.slice().reverse().forEach(item => { //i used the slice method
//in order to avoid mutating
//the original variable
obj = { ...obj,
...{
value: item,
rest: obj
}
};
})
console.log(obj)
Related
I have an array of objects. Each object has a key quantity and value. I want to duplicate each object in the array based on its quantity. Next, I want to manipulate only one of the duplicated object in the array. But on manipulating value of 1 object, value of all duplicated objects change. Here is my code:
let arr = [
{ id: 1, quantity: 3, value: 10 },
{ id: 2, quantity: 1, value: 5 },
{ id: 2, quantity: 5, value: 5 },
];
const newArr = [];
for (const a of arr) {
if (a.quantity > 1) {
let quantity = a.quantity;
a.quantity = 1;
while (quantity--) {
newArr.push(a);
}
}
}
arr = newArr;
arr[0].value = 1;
When I changed the value of arr[0] to 1, value field of arr[1] and arr[2] also changed to 1.
I have tried copying the object using spread operator and JSON.parse(JSON.parse()), but none has worked.
Because newArr.push(a) .a push to newArr ref to element of arr
You can edit same as :
let arr = [
{ id: 1, quantity: 3, value: 10 },
{ id: 2, quantity: 1, value: 5 },
{ id: 2, quantity: 5, value: 5 },
]
const newArr = []
for (const a of arr) {
if (a.quantity > 1) {
let quantity = a.quantity;
a.quantity = 1;
while (quantity--) {
newArr.push({...a})
}
}
}
arr = [...newArr]
arr[0].value = 1
console.log(arr)
// example for Memory Management
let a = { id: 1, quantity: 3, value: 10 }
let b = { id: 1, quantity: 3, value: 10 }
let c = arr[0]
let d = {...arr[0]}
console.log(a === arr[0]) // false : different allocates memory for contain value
console.log(a === b) // false : different allocates memory for contain value
console.log(c === arr[0]) // true : refer to a memory
console.log(d === arr[0]) // false : different allocates memory for contain value
I have an array that looks like this,
['event_tag', 'workflow_tag', 'created_timestamp', 'success']
and an array of objects where the object looks like,
{
"created_timestamp": "2022-04-01T13:14:53.028002Z",
"workflow_tag": "dj807",
"event_tag": "refresh",
"success": true
}
What I am wanting to do is make the above object and any other objects in that array match the order of the values in the first array so the finished object should look like,
{
"event_tag": "refresh",
"workflow_tag": "dj807",
"created_timestamp": "2022-04-01T13:14:53.028002Z",
"success": true
}
I have tried the following so far,
const keys = ['event_tag', 'workflow_tag', 'created_timestamp', 'success'];
newRowData = parsedRows.reduce((obj, v) => {
obj[v] = keys[v];
return obj
}, {});
But this returns,
{[object Object]: undefined}
You could order the keys by constructing a new object inside of an Array#map:
const parsedRows = [ { a: 1, c: 3, d: 4, b: 2, }, { b: 6, a: 5, c: 7, d: 8, }, { d: 12, b: 10, a: 9, c: 11, }, ];
const order = ['a', 'b', 'c', 'd'];
let newData = parsedRows.map(row => {
let newRow = {};
for (let key of order) {
newRow[key] = row[key];
}
return newRow;
});
console.log(newData);
Instead of iterating over Rows, Iterate on keys either map/reduce.
const keys = ["event_tag", "workflow_tag", "created_timestamp", "success"];
const obj = {
created_timestamp: "2022-04-01T13:14:53.028002Z",
workflow_tag: "dj807",
event_tag: "refresh",
success: true,
};
const res = Object.assign({}, ...keys.map((key) => ({ [key]: obj[key] })));
console.log(res)
I have an array of objects like this:
const arrayOfObjects = [
{ A: 1, B: 2, C: 3 },
{ A: 3, B: 4, C: 1 }
]
And another array which is called "headers"
const headers = [
['A', 'B'],
['C']
]
I have to create an array similar to the first one but, with those objects splited by what headers have in it's arrays.
This should be the goal:
const result = [
[
{ A: 1, B: 2 },
{ C: 3 }
],
[
{ A: 3, B: 4 },
{ C: 1 }
]
]
I tried by doing a "base" array with:
const baseArray = []
headers.forEach((header) => {
const objFromHeader = {};
header.forEach((head) => {
objFromHeader[head] = 0;
});
baseArray.push(objFromHeader);
});
That will give me the result array but with 0 values for each key.
And then loop for the first array and put inside another array the base array with the correct values.
Then I wanted to fill each key according to the value that comes from arrayOfObjects but here is where I can't see how could I loop that array of objects and put the correct value. The only problem with that approach is that the result array will have some 0 values that come from the initiation array that I'm using, it would be better to me to only put the objects that actually have values and not 0 (I was thinking on another function to delete those keys with value = 0...)
How could I achieve it in a better way?
Fiddle:
https://jsfiddle.net/pmiranda/Lpscz6vt/
When iterating over an object, use findIndex on the headers to identify which index in the headers array the property being iterated over should go into. Create an object there if it doesn't exist yet, and set the property.
const arrayOfObjects = [
{ A: 1, B: 2, C:3 },
{ A: 3, B: 4, C:1 }
];
const headers = [
['A', 'B'],
['C']
];
const toResultItem = (object) => {
const resultItem = [];
for (const [key, value] of Object.entries(object)) {
const headersIndex = headers.findIndex(arr => arr.includes(key));
resultItem[headersIndex] ??= {};
resultItem[headersIndex][key] = value;
}
return resultItem;
};
console.log(arrayOfObjects.map(toResultItem));
const arrayOfObjects = [
{ A: 1, B: 2, C: 3 },
{ A: 3, B: 4, C: 1 },
];
const headers = [['A', 'B'], ['C', 'D']];
const result = arrayOfObjects.map((obj) =>
headers.map((header) =>
header.reduce((acc, key) => {
acc[key] = obj[key];
return Object.keys(acc).reduce((newAcc, key) => {
if (acc[key]) {
newAcc[key] = acc[key];
}
return newAcc;
}
, {});
}, {})
)
);
console.log(result);
Array.forEach implementation
Logic
Loop through arrayOfObjects array.
Inside that, loop through headers array.
Inside that, loop through each array in the headers array.
Create an empty object and assign the property from nodes in headers array with values from objects in arrayOfObjects array.
const arrayOfObjects = [
{ A: 1, B: 2, C: 3 },
{ A: 3, B: 4, C: 1 }
];
const headers = [
['A', 'B'],
['C']
];
const baseArray = []
arrayOfObjects.forEach((obj) => {
const childNode = [];
headers.forEach((head) => {
const node = {};
head.forEach((key) => node[key] = obj[key]);
childNode.push(node);
});
baseArray.push(childNode);
});
console.log(baseArray)
Array.map and Array.reduce implementation.
Using the same logic implementes in the above solution, we can rewrite this using Array.map and Array.reduce as below.
const arrayOfObjects = [
{ A: 1, B: 2, C: 3 },
{ A: 3, B: 4, C: 1 }
];
const headers = [
['A', 'B'],
['C']
];
const output = arrayOfObjects.map((obj) => {
return headers.map((header) => {
return header.reduce((acc, curr) => {
acc[curr] = obj[curr];
return acc;
}, {});
})
})
console.log(output);
I have a nested object look like this:
let obj = {
F:{
asian: {
"35-44": 1,
"55-": 1,
},
"asian/black": {
"0-24": 1,
"35-44": 1,
"45-54": 2,
},
},
M:{
asian: {
"35-44": 1,
"55-": 1,
},
white: {
"0-24": 1,
"35-44": 1,
"45-54": 2,
},
},
}
And I want to flatten the object to this:
res = {
F: 6,
M: 6,
asian: 4,
"asian/black": 4,
white: 4,
"0-24": 2,
"35-44": 4,
"45-54": 4,
"55-": 2,
}
That every value in res should be the sum of the deepest object values(F, M) and object values with the same key(0-24, 35-44...). I feel this can be done using recursion and just can't get it right. The code I write:
let returnVal = 0
const flatten = (obj, prefix = '', res = {}) => {
return Object.entries(obj).reduce((r, [key, val]) => {
if(typeof val === 'object'){
flatten(val, key, r)
} else {
res[key] = val
returnVal = val;
}
if (key in res) {
res[key] += returnVal
} else {
res[key] = 0
res[key] += returnVal
}
return r
}, res)
}
console.log(flatten(obj))
it will output:
result = {
"0-24": 2,
"35-44": 2,
"45-54": 4,
"55-": 2,
F: 2,
M: 2,
asian: 2,
"asian/black": 2,
white: 2,
}
F, M, and some other keys are not correct. Thanks!
Another, perhaps simpler, approach is as follows:
const consolidate = (obj, path = [], results = {}) =>
Object .entries (obj) .reduce ((results, [k, v]) =>
Object (v) === v
? consolidate (v, [...path, k], results)
: [...path, k] .reduce (
(results, n) => ({...results, [n] : (results[n] || 0) + v}),
results
),
results)
const data = {F: {asian: {"35-44": 1, "55-": 1}, "asian/black": {"0-24": 1, "35-44": 1, "45-54": 2}}, M: {asian: {"35-44": 1, "55-": 1}, white: {"0-24": 1, "35-44": 1, "45-54": 2}}}
console .log (consolidate (data))
.as-console-wrapper {min-height: 100% !important; top: 0}
We recursively track paths taken through the object, such as ['F', 'asian/black', '45-54'] or ['M', 'white'] or simply ['f'] as well as an object containing the final results. When we the value at the current node is an object, we recur, adding the current property name to the path. When it's not (for this data it must therefore hit a number), we hit a base case in which we take each node in the current path, and update the results object by adding that number to the value for the node in the results object, or setting it to the current value if that value doesn't exist.
There is a potential issue with the default parameters, as described in another Q & A. If someone tried to map the consolidate function directly over an array of input objects, it would fail. If this is a concern, it's easy enough to swap the default parameters for a wrapper function:
const _consolidate = (obj, path, results) =>
Object .entries (obj) .reduce ((results, [k, v]) =>
Object (v) === v
? _consolidate (v, [...path, k], results)
: [...path, k] .reduce (
(results, n) => ({...results, [n] : (results[n] || 0) + v}),
results
),
results)
const consolidate = (obj) =>
_consolidate (obj, [], {})
const data = {
F: {
asian: {
"35-44": 1,
"55-": 1,
},
"asian/black": {
"0-24": 1,
"35-44": 1,
"45-54": 2,
},
},
M: {
asian: {
"35-44": 1,
"55-": 1,
},
white: {
"0-24": 1,
"35-44": 1,
"45-54": 2,
},
},
};
const isObject = obj => Object.prototype.toString.call(obj) === "[object Object]";
function nestKeys(obj, parent = "") {
return Object.keys(obj).map(key => {
const k = parent.length ? [parent, key].join(".") : key;
if (!isObject(obj[key])) {
return k;
}
return nestKeys(obj[key], k);
}).flat();
}
function flatObj(obj) {
const map = {};
const keys = nestKeys(obj);
keys.forEach(nestedKey => {
const splited = nestedKey.split(".");
const val = splited.reduce((acc, cur) => acc[cur], obj);
splited.forEach(k => {
map[k] = (map[k] || 0) + val;
})
});
return map;
}
console.log(flatObj(data));
I'm trying to write a function that takes an array of objects, and an unlimited number of arrays, and combines them to form a single object. The inputs would follow this pattern:
let x = [{ name: 'Tom' }, { name: 'John' }, { name: 'Harry' }];
let y = [[1, 2, 3], 'id'];
let z = [['a', 'b', 'c'], 'value'];
combine(x, y, z);
With the second element of y and z acting as the object key. Using these arguments, the function should return the following array:
[
{
name: 'Tom',
id: 1,
value: 'a'
},
{
name: 'John',
id: 2,
value: 'b'
},
{
name: 'Harry',
id: 3,
value: 'c'
},
]
The index of the current object should be used to get the correct element in the array. I have made an attempt at the problem:
function combine(object, ...arrays) {
return object.map((obj, index) => {
let items = arrays.map(arr => ({
[arr[1]]: arr[0][index]
}));
return Object.assign({}, obj, { items });
});
}
This almost does the job, but results in the array items being hidden inside a nested items array, How can I solve this?
You had been assigning an object of object, and the result was a new object with the element items inside (another feature of object literal).
This approach use reduce instead of map and direct assign instead of object literal.
function combine(object, ...arrays) {
return object.map((obj, index) => {
const items = arrays.reduce((acc, arr) => {
acc[arr[1]] = arr[0][index] ;
return acc;
}, {});
return Object.assign({}, obj, items);
});
}
const x = [{ name: 'Tom' }, { name: 'John' }, { name: 'Harry' }];
const y = [[1, 2, 3], 'id'];
const z = [['a', 'b', 'c'], 'value'];
combine(x, y, z);
You can also use the spread operator in the Object.assign, like this:
function combine(object, ...arrays) {
return object.map((obj, index) => {
let items = arrays.map(arr => ({
[arr[1]]: arr[0][index]
}));
return Object.assign({}, obj, ...items);
});
}
This almost does the job, but results in the array items being hidden inside a nested items array
The problem is that items is an array, whereas you only need the current item inside of that particular map callback. No need to nest loops here.
Also I would recommend avoiding multiple properties per combine call. The resulting code would look like this:
function combine(objects, [values, key]) {
return objects.map((o, i) =>
Object.assign({[key]: values[i]}, o)
);
}
combine(combine(x, y), z);
If you then have multiple extensions to do, you can also use
[y, z].reduce(combine, x)
With map and computed keys, you can achieve this.
Here's a working example:
let x = [{
name: 'Tom'
}, {
name: 'John'
}, {
name: 'Harry'
}];
let y = [[1, 2, 3], 'id'];
let z = [['a', 'b', 'c'], 'value'];
let result = [];
x.map(function (el, index) {
result.push(el);
let index = result.length -1;
result[index][y[1]] = y[0][index];
result[index][z[1]] = z[0][index];
});
console.log(result);