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Dynamic keys and properties in object [duplicate]

Suppose I have an array of object:
const apple = [{"bookName" :'Harry Pottar',part:"1"},{"bookName" :'Harry Pottar',part:"2"},
{"bookName": 'LOTR',part:"1"},{"bookName": 'LOTR',part:"2"},{"bookName": 'LOTR',part:"3"}]
I want to get count of all common values along with the value name as :
Expected O/P : [{"Harry Pottar":2},{"LOTR":3"}]
For this I tried as:
const id = "Harry Pottar";
const count = array.reduce((acc, cur) => cur.bookName === id ? ++acc : acc, 0);
As this gives the count, by this I can get count for each bookName. But how can I achieve my expected O/P scenario.
If anyone needs any further information please do let me know.

Good to see you know about .reduce! You’re pretty close, just need to save the result to a hashmap (plain object in JS).
const array = [{"bookName" :'Harry Pottar',part:"1"},{"bookName" :'Harry Pottar',part:"2"},{"bookName": 'LOTR',part:"1"},{"bookName": 'LOTR',part:"2"},{"bookName": 'LOTR',part:"3"}]
const result = array.reduce((acc, item) => {
const key = item.bookName
if (!acc.hasOwnProperty(key)) {
acc[key] = 0
}
acc[key] += 1
return acc
}, {})
// not sure why you want the result to be multiple objects. But here you go:
const output = Object.entries(result).map(([key, value])=> ({ [key]: value }))

Create a map from your data keyed by the book names, where the corresponding values are the objects you want in the output, with the count set to zero (you can use the computed property name syntax for the object's dynamic property). Then iterate the data again to increment the counters. Finally extract the values from the map into an array:
const apple = [{"bookName" :'Harry Pottar',part:"1"},{"bookName" :'Harry Pottar',part:"2"},
{"bookName": 'LOTR',part:"1"},{"bookName": 'LOTR',part:"2"},{"bookName": 'LOTR',part:"3"}];
let map = new Map(apple.map(({bookName}) => [bookName, { [bookName]: 0 }]));
for (let {bookName} of apple) map.get(bookName)[bookName]++;
let result = Array.from(map.values());
console.log(result);

You were pretty close. You don't necessarily need to have those objects in an array though. Just have an object with the booknames as the property keys. It would make it easier to manage.
If you then want to create an array of objects from that data you can use map over the Object.entries of that object.
const apple = [{"bookName" :'Harry Pottar',part:"1"},{"bookName" :'Harry Pottar',part:"2"},{"bookName": 'LOTR',part:"1"},{"bookName": 'LOTR',part:"2"},{"bookName": 'LOTR',part:"3"}];
const out = apple.reduce((acc, { bookName }) => {
// If the property doesn't exist, create it
// and set it to zero, otherwise increment the value
// of the existing property
acc[bookName] = (acc[bookName] || 0) + 1;
return acc;
}, {});
console.log(out);
const result = Object.entries(out).map(([ key, value ]) => {
return { [key]: value };
});
console.log(result);

How i can to convert array to object of array in react?

I have a data in array
["Avengers","Batman","Spiderman","IronMan"]
how I can to covert to below
{"Avenger":"Avenger","Batmane":"Batman","Spiderman":"Spiderman","Ironman":"Ironman"}

You can do it like this:
let arr = ["Avengers","Batman","Spiderman","IronMan"];
let obj = arr.reduce((acc, item)=> ({...acc, [item]: item}) , {});
console.log(obj);

Someone else mentioned reduce, but I recommend against, copying objects at every iteration.
Here's a more performant approach.
const arr = ["Avengers","Batman","Spiderman","IronMan"];
const obj = {};
for (const el of arr) {
obj[el] = el;
}
console.log(obj);

You can use reduce to convert array to object.
You can see some examples in here Convert Array to Object

Find Unique value from an array based on the array's string value (Javascript)

so I want to find unique values from an array.
so for example I have this array:
const mainArr = ['shape-10983', 'size-2364', 'size-7800', 'size-4602', 'shape-11073', 'size-15027', 'size-15030', 'size-15033', 'height-3399', 'height-5884']
so I want to find the first matching value for each unique item.
for example, in the array, I have two strings with the shape prefix, six items with the size prefix, and two items with the height prefix.
so I want to output to be something like
const requiredVal = ["shape-10983", "size-2364", "height-3399"]
I want only the first value from any set of different values.

the simplest solution will be to iterate on the list and storing what you got in a dictionary
function removeSimilars(input) {
let values = {};
for (let value of input) {//iterate on the array
let key = value.splitOnLast('-')[0];//get the prefix
if (!(key in values))//if we haven't encounter the prefix yet
values[key] = value;//store that the first encounter with the prefix is with 'value'
}
return Object.values(values);//return all the values of the map 'values'
}
a shorter version will be this:
function removeSimilars(input) {
let values = {};
for (let value of input)
values[value.splitOnLast('-')[0]] ??= value;
return Object.values(values);
}

You could split the string and get the type and use it aks key for an object along with the original string as value. At result take only the values from the object.
const
data = ['shape-10983', 'size-2364', 'size-7800', 'size-4602', 'shape-11073', 'size-15027', 'size-15030', 'size-15033', 'height-3399', 'height-5884'],
result = Object.values(data.reduce((r, s) => {
const [type] = s.split('-', 1);
r[type] ??= s;
return r;
}, {}));
console.log(result);

If, as you mentioned in the comments, you have the list of prefixes already available, then all you have to do is iterate over those, to find each first element that starts with that prefix in your full list of possible values:
const prefixes = ['shape', 'size', 'height'];
const list = ['shape-10983', 'size-2364', 'size-7800', 'size-4602', 'shape-11073', 'size-15027', 'size-15030', 'size-15033', 'height-3399', 'height-5884']
function reduceTheOptions(list = [], prefixes = [], uniques = []) {
prefixes.forEach(prefix =>
uniques.push(
list.find(e => e.startsWith(prefix))
)
);
return uniques;
}
console.log(reduceTheOptions(list, prefixes));

Try this:
function getRandomSet(arr, ...prefix)
{
// the final values are load into the array result variable
result = [];
const randomItem = (array) => array[Math.floor(Math.random() * array.length)];
prefix.forEach((pre) => {
result.push(randomItem(arr.filter((par) => String(par).startsWith(pre))));
});
return result;
}
const mainArr = ['shape-10983', 'size-2364', 'size-7800', 'size-4602', 'shape-11073', 'size-15027', 'size-15030', 'size-15033', 'height-3399', 'height-5884'];
console.log("Random values: ", getRandomSet(mainArr, "shape", "size", "height"));

I modified the #ofek 's answer a bit. cuz for some reason the ??= is not working in react project.
function removeSimilars(input) {
let values = {};
for (let value of input)
if (!values[value.split("-")[0]]) {
values[value.split("-")[0]] = value;
}
return Object.values(values);
}

create a new array and loop over the first array and check the existing of element before in each iteration if not push it to the new array

ES6 Filtering objects by unique attribute

I've an array of errors, each error has a non-unique param attribute.
I'd like to filter the array based on whether the param has been seen before.
Something like this:
const filteredErrors = [];
let params = [];
for(let x = 0; x < errors.length; x++) {
if(!params.includes(errors[x].param)) {
params.push(errors[x].param);
filteredErrors.push(errors[x]);
}
}
But I've no idea how to do this in ES6.
I can get the unique params const filteredParams = Array.from(new Set(errors.map(error => error.param)));
but not the objects themselves.
Pretty sure this is just a weakness in my understanding of higher order functions, but I just can't grasp it

You could destrucure param, check against params and add the value to params and return true for getting the object as filtering result.
As result you get an array of first found errors of the same type.
const
params = [],
filteredErrors = errors.filter(({ param }) =>
!params.includes(param) && params.push(param));

Instead of an array you can make use of an object to keep a map of existing values and make use of filter function
let params = {};
const filteredErrors = errors.filter(error => {
if(params[error.param]) return false;
params[error.param] = true;
return true;
});

i'd probably do it like this with a reduce and no need for outside parameters:
const filteredErrors = Object.values(
errors.reduce((acc, val) => {
if (!acc[val.param]) {
acc[val.param] = val;
}
return acc;
}, {}))
basically convert it into an object keyed by the param with the object as values, only setting the key if it hasn't been set before, then back into an array of the values.
generalized like so
function uniqueBy(array, prop) {
return Object.values(
array.reduce((acc, val) => {
if (!acc[val[prop]]) {
acc[val[prop]] = val;
}
return acc;
}, {}))
}
then just do:
const filteredErrors = uniqueBy(errors, 'param');

If your param has a flag identifier if this param has been seen before then you can simply do this.
const filteredErrors = errors.filter(({ param }) => param.seen === true);
OR
const filteredErrors = errors.filter((error) => error.param.seen);
errors should be an array of objects.
where param is one of the fields of the element of array errors and seen is one of the fields of param object.

You can do it by using Array.prototype.reduce. You need to iterate through the objects in the array and keep the found params in a Set if it is not already there.
The Set.prototype.has will let you find that out. If it is not present in the Set you add it both in the Set instance and the final accumulated array, so that in the next iteration if the param is present in your Set you don't include that object:
const errors = [{param: 1, val: "err1"}, {param: 2, val: "err2"}, {param: 3, val: "err3"}, {param: 2, val: "err4"}, {param: 1, val: "err5"}];
const { filteredParams } = errors.reduce((acc, e) => {
!acc.foundParams.has(e.param) && (acc.foundParams.add(e.param) &&
acc.filteredParams.push(e));
return acc;
}, {foundParams: new Set(), filteredParams: []});
console.log(filteredParams);

JavaScript - Filter <key,value> Object by key

I am looking for a short and efficient way to filter objects by key, I have this kind of data-structure:
{"Key1":[obj1,obj2,obj3], "Key2":[obj4,obj5,obj6]}
Now I want to filter by keys, for example by "Key1":
{"Key1":[obj1,obj2,obj3]}

var object = {"Key1":[1,2,3], "Key2":[4,5,6]};
var key1 = object["Key1"];
console.log(key1);

you can use the .filter js function for filter values inside an object
var keys = {"Key1":[obj1,obj2,obj3], "Key2":[obj4,obj5,obj6]};
var objectToFind;
var keyToSearch = keys.filter(function(objects) {
return objects === objectToFind
});
The keyToSearch is an array with all the objects filter by the objectToFind variable.
Remember, in the line return objects === objectToFind is where you have to should your statement. I hope it can help you.

You can create a new object based on some custom filter criteria by using a combination of Object.keys and the array .reduce method. Note this only works in es6:
var myObject = {"Key1":["a","b","c"], "Key2":["e","f","g"]}
function filterObjectByKey(obj, filterFunc) {
return Object.keys(obj).reduce((newObj, key) => {
if (filterFunc(key)) {
newObj[key] = obj[key];
}
return newObj;
}, {});
}
const filteredObj = filterObjectByKey(myObject, x => x === "Key1")
console.log(filteredObj)

Not sure what exactly are you trying to achieve, but if you want to have a set of keys that you would like to get the data for, you have quite a few options, one is:
var keys = ['alpha', 'bravo'];
var objectToFilterOn = {
alpha: 'a',
bravo: 'b',
charlie: 'c'
};
keys.forEach(function(key) {
console.log(objectToFilterOn[key]);
});