Delete multiple keys from array of Object - javascript

Let's say we have an array of object:
var obj = [{a: 1, b: 2, c: 3, d: 4, e: 5 },{a: 6, b: 7, c:
8, d: 9, e: 0 }];
and we want to delete key c,e from both of the objects.
How can it be done? One of the methods I found is:
['c', 'e'].forEach(e => delete obj[e]); //for object
Is there any other way so we don't have to use double for loop.

One way to do it is to use .map() together with object destructuring:
var obj = [
{ a: 1, b: 2, c: 3, d: 4, e: 5 },
{ a: 6, b: 7, c: 8, d: 9, e: 0 },
];
var newObj = obj.map(({ c, e, ...rest }) => rest);
console.log(newObj)
This will create a new array with new objects which contain all of the other keys except for c and e.

You have 2 options to resolve it:
By using object destructuring: map(({ a,b,c,d,e }) => ({a,b,d})
Enhance option 1 by using using [Rest parameters] { c, e, ...rest }
Object destructuring like below
const obj = { a: 1, b: 2, c: 3, d: 4, e: 5 } var {c, e} = obj; // c = 3, e = 5
With option 2, you will have c,e implicit name and the remaining items named rest. After that, you just need to get rest items.
Option 1
var obj =
[
{ a: 1, b: 2, c: 3, d: 4, e: 5 },
{ a: 6, b: 7, c: 8, d: 9, e: 0 },
];
console.log(obj.map(({ a,b,c,d,e }) => ({a,b,d})));
Option 2
var obj =
[
{ a: 1, b: 2, c: 3, d: 4, e: 5 },
{ a: 6, b: 7, c: 8, d: 9, e: 0 },
];
console.log(obj.map(({ c, e, ...rest }) => rest));
// ...rest: the same as `a,b,d`

Related

problem with reduce and memoisation in javascript hardstructure

i have to do a task, where i need to iterate over hardstructure with nested functions arrays objects and other data types. get all the numbers there are in string or not in string into the array and then with reduce method i need to calculate their sum, after calculating their sum i need to do memoisation on this function. but something doesnt work with my reduce even though i have written the most simple task there is, calculating the sum of numbers. my reduce doesnt really calculate the right way it skips some parts of the structure and doesnt gather all of the nubmers also it doesnt really calculate right i think
const ex1 = () => ({ a: 13 });
const ex2 = () => [1, 2, 3, 4, 5, "a,,,,,,", 2, 2, 2];
const ex3 = () => [...ex2()];
const ex4 = new Set([1, 2, 3, 4]);
const hardStructure = [
{
a: 1,
b: "2",
c: [
{
a: "123",
b: "#333z$34",
c: "122,333,4444,5555",
z: ex4,
d: [
[
123,
1,
"1111",
23323,
1222,
55,
[1212, 1212, 1212],
{
a: 111,
b: null,
c: () => 111,
d: 22,
e: "e",
f: () => "fffqqq",
},
],
[
2212,
1,
"111211",
23,
121,
22,
[33, 3, 3],
{
a: 3,
b: null,
c: () => 11221,
d: 2112,
e: "e11",
f: () => "fffqqq",
g: 2,
},
],
[
11,
22,
"dsds",
{
a: {
b: {
c: {
d: {
a: 1,
b: [ex1()],
c: {
a: {
b: {
c: {
d: {
a: new Map([
["a2134", 2123123],
["b", 3],
["c", 3],
]),
b: ex2,
c: [...ex3(), "1", 1],
},
},
},
},
},
},
},
},
},
},
],
],
},
],
},
{
d: [
[
123,
1,
"1111",
23323,
1222,
55,
[121322332, 12132322, 12323212],
{
a: 111,
b: null,
c: () => 1123231,
d: 22,
e: "e",
f: () => "fffqqq",
},
],
[
2212,
1,
"111211",
23,
121,
22,
[33, 3, 3],
{
a: 3,
b: null,
c: () => 1123221,
d: 211,
e: "e1231",
f: () => "fffqq1232312123q",
g: 2123,
},
],
[
11,
22,
"dsds",
{
a: {
b: {
c: {
d: {
a: 1,
b: [ex1()],
c: {
a: {
b: {
c: {
d: {
a: new Map([
[true, 222312],
[2, 322],
["c2", 32],
[() => {}, 32],
]),
b: ex2,
c: [...ex3(), "1121123", 1],
},
},
},
},
},
},
},
},
},
},
],
],
},
{
a: {
b: {
c: {
d: {
a: 112312,
b: [1],
c: {
a: {
b: {
c: {
d: {
a: "",
b: "",
c: "",
v: "v12312323",
},
},
},
},
},
},
},
},
},
},
];
const numbersArr = [];
const iterate = (hardStructure) => {
if (hardStructure === null || hardStructure === undefined) {
return [];
}
if (
hardStructure.constructor === new Set().constructor ||
hardStructure.constructor === new Map().constructor
) {
console.log("console from map or set");
hardStructure.forEach((element) => {
// console.log("123", element);
return iterate(element);
});
}
if (typeof hardStructure === "function") {
return iterate(hardStructure());
}
if (Array.isArray(hardStructure)) {
hardStructure.map((items) => {
return iterate(items);
});
}
if (typeof hardStructure === "object" && !Array.isArray(hardStructure)) {
for (let key in hardStructure) {
// console.log(hardStructure[key]);
return iterate(hardStructure[key]);
}
}
if (typeof hardStructure !== "string") {
const stringItem = String(hardStructure);
for (let i = 0; i < stringItem.length; i++) {
if (!isNaN(+stringItem)) {
numbersArr.push(+stringItem);
}
}
}
for (let i = 0; i < hardStructure.length; i++) {
// console.log(i);
if (!isNaN(+hardStructure[i])) {
// console.log("12345678910", isNaN(+hardStructure[2]));
numbersArr.push(+hardStructure[i]);
}
}
const sumWithInitial = numbersArr.reduce((accumulator, currentValue) => {
console.log(accumulator,currentValue)
return accumulator + currentValue;
},0);
// console.log(numbersArr)
console.log(sumWithInitial);
return sumWithInitial;
};
iterate(hardStructure);
Your requirements aren't entirely clear, especially as to handling of String and Function properties. This solution assumes that you want to call functions and that you can use parseInt for Strings. If you need to change that, it should be clear enough how and where to do so:
const sumNumbers = (xs) =>
xs == null
? 0
: xs .constructor == String
// ? parseInt (xs, 10) || 0 // original version not enough. Below might not be so either
? xs .includes (',') ? sumNumbers (xs .split (',')) : Number (xs .replaceAll (/\D/g, ''))
: xs .constructor == Number
? xs
: xs .constructor === Array
? xs .map (sumNumbers) .reduce ((a, b) => a + b, 0)
: xs .constructor === Set
? sumNumbers ([...xs])
: xs .constructor === Map
? sumNumbers ([...xs .values()])
: xs .constructor === Function
? sumNumbers (xs ()) // or just 0?
: xs .constructor == Object
? sumNumbers (Object .values (xs))
// TODO: Other types possible here?
: 0
const ex1 = () => ({a: 13}),
ex2 = () => [1, 2, 3, 4, 5, "a,,,,,,", 2, 2, 2],
ex3 = () => [...[1, 2, 3, 4, 5, "a,,,,,,", 2, 2, 2]],
ex4 = new Set ([1, 2, 3, 4]),
hardStructure = [{a: 1, b: "2", c: [{a: "123", b: "#333z$34", c: "122,333,4444,5555", z: ex4, d: [[123, 1, "1111", 23323, 1222, 55, [1212, 1212, 1212], {a: 111, b: null, c: () => 111, d: 22, e: "e", f: () => "fffqqq"}], [2212, 1, "111211", 23, 121, 22, [33, 3, 3], {a: 3, b: null, c: () => 11221, d: 2112, e: "e11", f: () => "fffqqq", g: 2}], [11, 22, "dsds", {a: {b: {c: {d: {a: 1, b: [{a: 13}], c: {a: {b: {c: {d: {a: new Map ([["a2134", 2123123], ["b", 3], ["c", 3]]), b: ex2, c: [...ex3(), "1", 1]}}}}}}}}}}]]}]}, {d: [[123, 1, "1111", 23323, 1222, 55, [121322332, 12132322, 12323212], {a: 111, b: null, c: () => 1123231, d: 22, e: "e", f: () => "fffqqq"}], [2212, 1, "111211", 23, 121, 22, [33, 3 , 3], {a: 3, b: null, c: () => 1123221, d: 211, e: "e1231", f: ()=> "fffqq1232312123q", g: 2123}], [11, 22, "dsds", {a: {b: {c: {d: {a: 1, b: [{a: 13}], c: {a: {b: {c: {d: {a: new Map ([[true, 222312], [2, 322], ["c2", 32], [() => {}, 32]]), b: ex2, c: [...ex3 (), "1121123", 1]}}}}}}}}}}]]}, {a: {b: {c: {d: {a: 112312, b: [1], c: {a: {b: {c: {d: {a: "", b: "", c: "", v: "v12312323"}}}}}}}}}}]
console .log (sumNumbers (hardStructure))
We have four base cases:
on a nil value (null or undefined), we return 0
on a Number, we return its value
on a String, we call parseInt on it and return the value. This is the part I think you would most likely need to change
on an unknown type (perhaps a regular expression or a date), we return 0
The others are recursive case:
for an Array, we recursively call our function on each element and then total them together.
for a Function, we call the function with no arguments, and recur on the result.
for our other known types (Object, Set, Map), we extract its values into an Array and recur on the result.

Find properties that are null for every JavaScript object in an array

For example, if I have a JavaScript array of objects such as:
var jsObjects = [
{a: 1, b: 2, c: null, d: 3, e: null},
{a: 3, b: null, c: null, d: 5, e: null},
{a: null, b: 6, c: null, d: 3, e: null},
{a: null, b: 8, c: null, d: 1, e: null}
];
I would expect the output to be ["c", "e"].
My current solution is to call a function for each column & loop through the jsObjects:
function isAllNull(col) {
var allNulls = true;
for (var i = 0; i < data.length; i++) {
if (jsObjects[i].col != null) {
allNulls = false;
break;
}
}
}
But I would like for this function to be more generic such that it will jsObjects with any number of arbitrary simple (i.e. not objects) properties. The objects in the array all have the same properties.
If you guarantee that each object in the array has the same properties then:
take the keys from the first object in the array
reduce the keys and test every key in the original array for null
if every key returns true then include the key in the output
Example:
var jsObjects = [
{a: 1, b: 2, c: null, d: 3, e: null},
{a: 3, b: null, c: null, d: 5, e: null},
{a: null, b: 6, c: null, d: 3, e: null},
{a: null, b: 8, c: null, d: 1, e: null}
];
function nullCols(arr) {
var keys = Object.keys(arr[0]);
var nulls = keys.reduce((output, key) => {
if (arr.every(item => item[key] === null)) {
output.push(key);
}
return output;
}, []);
return nulls;
}
console.log(nullCols(jsObjects));

Finding all the keys in the array of objects

Given that I have an array that is return from database that contains object,
var jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4, c: 66},
{a: 5, b: 6, c: 55, d: 66},
{a: 7, b: 8, c: 12, e: 15}
];
How can I get all the keys of the object? I've been using this to obtain the keys, however I notice that index 0 wont always have all the keys. Hence problem lays.
let columns = Object.keys(jsObjects[0]),
However, the first index won't always have all the columns.
My desired output:
["a", "b", "c", "d", "e"]
Sets are good at removing duplicates:
const jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4, c: 66},
{a: 5, b: 6, c: 55, d: 66},
{a: 7, b: 8, c: 12, e: 15}
];
const keys = [...new Set(jsObjects.flatMap(Object.keys))];
console.log(keys);
You could create an object with the count of the keys and get the keys from counts.
const
objects = [{ a: 1, b: 2 }, { a: 3, b: 4, c: 66 }, { a: 5, b: 6, c: 55, d: 66 }, { a: 7, b: 8, c: 12, e: 15 }],
result = Object.keys(objects.reduce((r, o) => {
Object.keys(o).forEach(k => r[k] = true);
return r;
}));
console.log(result);
You can use a Set(), which is like an array with the exception that it doesn't allow multiple occurances of elements.
var jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4, c: 66},
{a: 5, b: 6, c: 55, d: 66},
{a: 7, b: 8, c: 12, e: 15}
];
var keys = new Set();
for(object of jsObjects) {
for(key in object) {
keys = keys.add(key);
}
}
for (const key of keys) {
console.log(key);
}
I tried this solution: iterating on jsObjects elements and pushing keys
into columns array if not present.
var jsObjects = [
{a: 1, b: 2},
{a: 3, b: 4, c: 66},
{a: 5, b: 6, c: 55, d: 66},
{a: 7, b: 8, c: 12, e: 15}
];
let columns = [];
jsObjects.forEach(
o => {
Object.keys(o).forEach(
t => {
if (columns.indexOf(t) < 0 ) {
columns.push(t);
}
}
)
}
)
console.log(columns);

How to group by multiple keys at the same time using D3?

This works, but I was wondering if there was a better way than creating a string with a and b and later splitting it:
const data = [
{ a: 10, b: 20, c: 30, d: 40 },
{ a: 10, b: 20, c: 31, d: 41 },
{ a: 12, b: 22, c: 32, d: 42 }
];
d3.rollups(
data,
x => ({
c: x.map(d => d.c),
d: x.map(d => d.d)
}),
d => `${d.a} ${d.b}`
)
.map(([key, values]) => {
const [a, b] = key.split(' ');
return {a, b, ...values};
});
// OUTPUT
// [
// {a: "10", b: "20", c: [30, 31], d: [40, 41]},
// {a: "12", b: "22", c: [32], d: [42]}
// ]
With d3 v7 released, there is now a better way to do this using the new d3.flatRollup.
const data = [
{ a: 10, b: 20, c: 30, d: 40 },
{ a: 10, b: 20, c: 31, d: 41 },
{ a: 12, b: 22, c: 32, d: 42 }
];
const result = d3.flatRollup(
data,
x => ({
c: x.map(d => d.c),
d: x.map(d => d.d)
}),
d => d.a,
d => d.b
);
console.log(result);
const flattened = result.map(([a, b, values]) => ({a, b, ...values}));
console.log(flattened);
<script src="https://cdn.jsdelivr.net/npm/d3-array#3.0.2/dist/d3-array.min.js"></script>
As you already know d3.rollups() will create nested arrays if you have more than one key:
If more than one key is specified, a nested Map [or array] is returned.
Therefore, as d3.rollups doesn't fit your needs, I believe it's easier to create a plain JavaScript function (I'm aware of "using D3" in your title, but even in a D3 code nothing forbids us of writing plain JS solutions where D3 has none).
In the following example I'm purposefully writing a verbose function (with comments) so each part of it is clear, avoiding more complex features which could make it substantially short (but more cryptic). In this function I'm using reduce, so the data array is looped only once. myKeys is the array of keys you'll use to rollup.
Here is the function and the comments:
function groupedRollup(myArray, myKeys) {
return myArray.reduce((a, c) => {
//Find the object in the acc with all 'myKeys' equivalent to the current
const foundObject = a.find(e => myKeys.every(f => e[f] === c[f]));
//if found, push the value for each key which is not in 'myKeys'
if (foundObject) {
for (let key in foundObject) {
if (!keys.includes(key)) foundObject[key].push(c[key]);
};
//if not found, push the current object with all non 'myKeys' keys as arrays
} else {
const copiedObject = Object.assign({}, c);//avoids mutation
for (let key in copiedObject) {
if (!keys.includes(key)) copiedObject[key] = [copiedObject[key]];
};
a.push(copiedObject);
};
return a;
}, [])
};
Here is the demo:
const data = [{
a: 10,
b: 20,
c: 30,
d: 40
},
{
a: 10,
b: 20,
c: 31,
d: 41
},
{
a: 12,
b: 22,
c: 32,
d: 42
}
];
const keys = ["a", "b"];
console.log(groupedRollup(data, keys))
function groupedRollup(myArray, myKeys) {
return myArray.reduce((a, c) => {
const foundObject = a.find(e => myKeys.every(f => e[f] === c[f]));
if (foundObject) {
for (let key in foundObject) {
if (!keys.includes(key)) foundObject[key].push(c[key]);
};
} else {
const copiedObject = Object.assign({}, c);
for (let key in copiedObject) {
if (!keys.includes(key)) copiedObject[key] = [copiedObject[key]];
};
a.push(copiedObject);
};
return a;
}, [])
};
And here is a demo with a more complex data:
const data = [{
a: 10,
b: 20,
c: 30,
d: 40,
e: 5,
f: 19
},
{
a: 10,
b: 55,
c: 37,
d: 40,
e: 5,
f: 19
},
{
a: 10,
b: 20,
c: 31,
d: 48,
e: 5,
f: 18
},
{
a: 80,
b: 20,
c: 31,
d: 48,
e: 5,
f: 18
},
{
a: 1,
b: 2,
c: 3,
d: 8,
e: 5,
f: 9
},
{
a: 10,
b: 88,
c: 44,
d: 33,
e: 5,
f: 19
}
];
const keys = ["a", "e", "f"];
console.log(groupedRollup(data, keys))
function groupedRollup(myArray, myKeys) {
return myArray.reduce((a, c) => {
const foundObject = a.find(e => myKeys.every(f => e[f] === c[f]));
if (foundObject) {
for (let key in foundObject) {
if (!keys.includes(key)) foundObject[key].push(c[key]);
};
} else {
const copiedObject = Object.assign({}, c);
for (let key in copiedObject) {
if (!keys.includes(key)) copiedObject[key] = [copiedObject[key]];
};
a.push(copiedObject);
};
return a;
}, [])
};
Finally, pay attention that this function will push duplicated values (in the above example d: [40, 40, 33]). If that's not what you want then just check for duplicates.
The approach below allows you to remove the split, but does not prevent the need to create a string for the compound key. In this case, using JSON.stringify({a: d.a, b: d.b}) instead of ${d.a} ${d.b}, allows for the map to return an object where the c and d properties can be assigned to the parse of the key.
This preserves some of the 'd3-ishness' of your question and the utility of rollups to deal with the creation of the arrays for c and d.
const data = [
{ a: 10, b: 20, c: 30, d: 40 },
{ a: 10, b: 20, c: 31, d: 41 },
{ a: 12, b: 22, c: 32, d: 42 }
];
const groups = d3.rollups(
data,
x => ({
c: x.map(d => d.c),
d: x.map(d => d.d)
}),
d => JSON.stringify({a: d.a, b: d.b}) // compare with `${d.a} ${d.b}`
).map(arr => Object.assign(JSON.parse(arr[0]), arr[1]));
console.log(groups);
.as-console-wrapper { max-height: 100% !important; top: 0; }
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.5.0/d3.min.js"></script>
The approach can accommodate the extensibility of #Gerado Furtado's answer, but I fear it's getting a little hectic:
const data = [
{a: 10, b: 20, c: 30, d: 40, e: 5, f: 19},
{a: 10, b: 55, c: 37, d: 40, e: 5, f: 19},
{a: 10, b: 20, c: 31, d: 48, e: 5, f: 18},
{a: 80, b: 20, c: 31, d: 48, e: 5, f: 18},
{a: 1, b: 2, c: 3, d: 8, e: 5, f: 9},
{a: 10, b: 88, c: 44, d: 33, e: 5, f: 19}
];
const keys = ["a", "e", "f"];
const groupedRollup = (data, keys) => {
const others = Object.keys(data[0])
.filter(k => !keys.includes(k)); // finds b, c, d as not part of compound key
return d3.rollups(
data,
x => Object.assign(
{},
...others.map(k => {
return {[k]: x.map(d => d[k])} // dynamically create reducer
})
),
d => JSON.stringify(
Object.assign(
{},
...keys.map(k => {
return {[k]: d[k]} // dynamically add keys
})
)
) // and stringify for compound key
).map(arr => Object.fromEntries( // sorting the output object
Object.entries( // keys in alpha order
Object.assign(JSON.parse(arr[0]), arr[1])).sort() // same approach
)
);
}
console.log(groupedRollup(data, keys));
.as-console-wrapper { max-height: 100% !important; top: 0; }
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.5.0/d3.min.js"></script>
There's some interesting talk about the introduction of use of InternMap in rollups and the associated functions - but I don't see either that it's ready, or that it's useful for what you are trying to do.

How to get some props of list array object by using reduce

I have list array object like:
let arr = [
{ a: 1, b: 2, c: 3, d: 4 },
{ a: 2, b: 3, c: 4, d: 5 },
{ a: 5, b: 6, c: 7, d: 8 }
]
and after using reduce()
// get props **b, c**
let arr_result = arr.reduce( ... )
// arr_result = [
// { b: 2, c: 3 },
// { b: 3, c: 4 },
// { b: 6, c: 7 }
// ]
use map.
let arr = [{
a: 1,
b: 2,
c: 3,
d: 4
},
{
a: 2,
b: 3,
c: 4,
d: 5
},
{
a: 5,
b: 6,
c: 7,
d: 8
}
]
const output = arr.map(({b, c}) => ({b, c}));
console.log(output);
You can use ES6(and beyond)'s object destructuring.
const arr = [
{ a: 1, b: 2, c: 3, d: 4 },
{ a: 2, b: 3, c: 4, d: 5 },
{ a: 5, b: 6, c: 7, d: 8 }
]
const res = arr.map(obj => {
const { b, c } = obj;
return { b, c };
});
console.log(res);
Since you asked to achieve this using reduce, here is the way. Pass an empty array as thisArg & inside reduce callback function create an object with required key and push it to the accumulator
let arr = [{
a: 1,
b: 2,
c: 3,
d: 4
},
{
a: 2,
b: 3,
c: 4,
d: 5
},
{
a: 5,
b: 6,
c: 7,
d: 8
}
];
let newArr = arr.reduce(function(acc, curr) {
acc.push({
b: curr.b,
c: curr.c
})
return acc;
}, [])
console.log(newArr)
If you want to use reduce:
const arr = [{a:1,b:2,c:3,d:4},{a:2,b:3,c:4,d:5},{a:5,b:6,c:7,d:8}];
const res = arr.reduce((a, { b, c }) => (a.push({ b, c }), a), []);
console.log(res);
.as-console-wrapper { max-height: 100% !important; top: auto; }
It's honestly a lot easier with map:
const arr = [{a:1,b:2,c:3,d:4},{a:2,b:3,c:4,d:5},{a:5,b:6,c:7,d:8}];
const res = arr.map(({ b, c }) => ({ b, c }));
console.log(res);
.as-console-wrapper { max-height: 100% !important; top: auto; }

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