Create a simple rank array using map function (JavaScript) - javascript

So essentially I have a JSON that it's in the format as so:
JSON= [
{username: foo, score: 12343},
{username: bar, score: 9432},
{username: foo-bar, score: 402, ...
]
I know that the JSON that I am getting back is already rank from highest to lowest, based on the scores.
How can I make an array that automatically inserts the rank position? For instance, I would like to see an output of :
[1, username: foo, score: 12343],
[2, username: bar, score: 9432],
[3, username: foo-bar, score: 402],...

Javascript got you covered already. An array always has indexes, though it starts at zero. If you want the best, just use
console.log(JSON[0]);
and if you insist on 1 being 1, try this
function getByRank(index) {
return JSON[index - 1];
}
so you will get the best with
console.log(getByRank(1)); // {username: "foo", score: 12343}
I think in your code the json is valid json, see the " around foo...

Your syntax seems off, but assuming that the JSON is:
JSON = [
{username: 'foo', score: 12343},
{username: 'bar', score: 9432},
{username: 'foo-bar', score: 402}
]
Since Arrays are 0 indexed and you have access to the current index in a .map method, you can do something along the following:
JSON = JSON.map(function (record, index) {
record.rank = index + 1;
return record;
})
This should give you the following output:
[
{ rank: 1, username: 'foo', score: 12343 },
{ rank: 2, username: 'bar', score: 9432},
{ rank: 3, username: 'foo-bar', score: 402}
]
Hope this helps.

Strictly from the point of view of your question, you already got the answer. I just want to enumerate some ideas, maybe they will be useful to some of you in the future:
First of all, JSON (JavaScript Object Notation) is an open-standard format that uses human-readable text to serialize objects, arrays, numbers, strings, booleans, and null. Its syntax, as the name states, is derived from JavaScript, but JSON is actually a text, a string.
A JSON string is (almost always) syntactically correct
JavaScript code.
Make sure you don't use the keyword "JSON" as the name of a variable, because JSON is actually an existing object in JavaScript, and it is used to encode to JSON format (stringify) and decode from JSON format (parse).
Just try JSON.stringify({a: 2, b: 3}); and JSON.parse('{"a":2,"b":3}'); in a JavaScript console.

Related

How to get second duplicate value rather than first value from JSON Array in React JS using lodash? [duplicate]

This question already has an answer here:
Lodash uniqBy update the latest value
(1 answer)
Closed 9 months ago.
I am working on one project where I need to remove duplicate values from JSON array object with some specification in react JS. I have tried to remove using _.uniqBy but in the output it took very first value from duplicate value which is I don't want.
Suppose You have an array JSON like:
[ { id: 1, name: 'bob' }, { id: 2, name: 'bill' }, { id: 1, name: 'alice' } ]
using _.uniqBy I got [ { id: 1, name: 'bob' }, { id: 2, name: 'bill' }] this output.
but I want [ { id: 2, name: 'bill' }, { id: 1, name: 'alice' } ] this output.
As you can see I want output whose name is alice not bob along with id:1.
Can anyone help me?
Thank you.
My first thought is to use a reduce, and shove the items in a map, then get the values:
Object.values(items.reduce((map, item) => ({ ...map, [item.id]: item }), {}))
This is probably not very efficient though if you're dealing with large arrays of have performance concerns.
It's a quick and dirty one-liner. If you want something more efficient I'd take a look at the lodash source code and tweak it to your needs or write something similar:
https://github.com/lodash/lodash/blob/2f79053d7bc7c9c9561a30dda202b3dcd2b72b90/.internal/baseUniq.js

How can I update some array entries to have multiple values?

I have an array as such:
arr = {
name: 1,
address: 1,
phone: 2,
email: 5,
};
I want to be able to add further information to this array, eg:
arr = {
name: 1 true,
address: 1 false,
phone: 2 true,
email: 5 true,
};
I've tried a few different things like:
arr.email[2] = true;
With no results (or errors).
Is there a way to do this? Or a better way of handling this issue?
I'm not entirely certain what you're going for here since you mention wanting an array ([]) but what you've shown in your question is an object ({}), but if I'm reading right you can accomplish this with an object where each key holds an array of values. That would look like:
const obj = {
name: [1],
address: [1],
phone: [2],
email: [5],
};
obj.email.push(true);
obj.email.push("whatever");
console.log(obj)
console.log(obj.email[1])
console.log(obj.email[2])
So obj is an object, but name, address, phone, and email are all arrays which you can extend as needed with array methods.
Original data structure doesn't allow you to add data the way you want. So you have to create the object with needed data structure at first. After this the original data should be moved to the new object and only after this you can add some new data.
newObj.name.push(origObj.name,true,"something1","something2");
newObj.address.push(origObj.address,false);
newObj.phone.push(origObj.phone,true);
newObj.email.push(origObj.email,true);
output
{
"name":[1,true,"something1","something2"],
"address":[1,false],
"phone":[2,true],
"email":[5,true]
}
original object
var origObj = {
name: 1,
address: 1,
phone: 2,
email: 5
};
new object
var newObj = {
name: [],
address: [],
phone:[],
email: []
};
You would need to assign a variable to your array and call a function...that way, each element could be classified (boolean, string, integer, etc.) For example,
const fruit = ['banana', 'apple', 'pear'];
console.log(fruit);

Is this JavaScript two dimensional array?

const monsters = {
'1': {
name: 'godzilla',
age: 250000000
},
'2': {
Name: 'manticore',
age: 21
}
}
I learn JavaScript from Codecademy, What does this code mean?
Is this two dimensional array? If not, what is it?
The data structure you are showing in your code example is not an array at all, it is an object. Arrays are defined using square brackets ([]) and their keys (indices) are not explicitly declared but rather assigned automatically.
So if you wrote your code like this, for example, you would have an array containing objects:
const monsters = [
{
name: 'godzilla',
age: 250000000
},
{
name: 'manticore',
age: 21
}
]
…so you could access the values by their array index, like so.
monsters[0].name; // godzilla
monsters[1].name; // manticore

Javascript arrays and objects: Get differences and merge them

So I have this scenario where I have a client-app which sends data (array of objects) to a server which then forwards the data to other clients connected to this server.
In the client-app, the data is constantly changing, meaning: Values change, new objects inside the array pop up, objects being removed, and so on ...
Now I want the other clients to always receive the latest data. And because I dont want the client-app to just push the whole new data to the server which then forwards the whole new data to the other clients, I decided to let the client-app only push the changes (using this library: https://www.npmjs.com/package/deep-object-diff).
The other clients then receive an array of objects with only the data that has actually changed and because they know the previous data array, I want them to "merge" the array of changes with the old data object.
My actual problem is the merging. I dont know how to properly do this. Especially if I have an array of objects without any key for the objects.
So my data looks something like this:
let data = [
{
name: 'Peter',
age: 26,
sID: 546589995544
},
{
name: 'John',
age: 33,
sID: 554589525469
}
];
Actually there's much more but well, thats the structure.
So if the diff library says, this are the changes:
let changes = {
{
age: 34,
sID: 554589525469
}
};
(notice that I now have an object of objects, not an array of objects. Thats what the diff-library returns)
I want the merged object to be
[
{
name: 'Peter',
age: 26,
sID: 546589995544
},
{
name: 'John',
age: 34,
sID: 554589525469
}
];
(John is now one year older)
So I totally believe that this would be much easier if I had a key to the objects as an identifier, but still I think there has to be a solution for exactly this scenario. And as you can see, the sID property could act as an identifier, its just not a key.
I would apprectiate if someone could point out how to do it in both cases (with and without a specific key for the objects)
You can use .find() to find the object within the array where values should be changed, Object.assign() to set the values
let data = [{
name: 'Peter',
age: 26,
sID: 546589995544
},
{
name: 'John',
age: 33,
sID: 554589525469
}
];
let changes = [{
age: 34,
sID: 554589525469
}];
for (let prop of changes) {
let {sID} = prop;
Object.assign(data.find(({sID: id}) => id === sID), prop)
}
console.log(data);
You could use a sId Map for fast lookup:
const byId = new Map( data.map( el => [el.sID, el]));
Then for every change we can find if the obj already exists, if not we add it, if yes we mutate:
changes.forEach(change => {
const res = byId.get( change.sID );
if( res ){
Object.assign( res, change);
}else{
data.push(change);
byId.set( change.sID, change);
}
});
Using lodash, you can accomplish this with unionBy :
const newData = _.unionBy(changes, data, 'sID'); // values from changes will be picked
This will pick objects from both the arrays based on sID and combine them into a single array.
If your changes data is object of objects , you can use Object.values to loop data value and merge same id data by Object.assign
let data = [
{
name: 'Peter',
age: 26,
sID: 546589995544
},
{
name: 'John',
age: 33,
sID: 554589525469
}
];
let changes = {
0:
{
age: 34,
sID: 554589525469
}
};
data.filter((idx,i)=>
Object.values(changes).forEach((index)=>
(index.sID == idx.sID) ? Object.assign(data[i],index) : null
)
);
console.log(data);

How to reference a specific object in an array of objects using jTemplates

I am using the excellent jTemplates plugin to generate content.
Given a data object like this...
var data = {
name: 'datatable',
table: [
{id: 1, name: 'Anne'},
{id: 2, name: 'Amelie'},
{id: 3, name: 'Polly'},
{id: 4, name: 'Alice'},
{id: 5, name: 'Martha'}
]
};
..I'm wondering if it is possible to directly specify an object in an array of objects using $T. (I'm hoping there is something like $T.table:3 available)
Currently the only way I can think of to access a specific object in an array is to do something like this...
{#foreach $T.table as record}
{#if $T.record$iteration == 3}
This is record 3! Name: {$T.record.name}
{#/if}
{#/for}
However that seems clumsy...
Any suggestions?
Thanks
With the data you posted, you can do this with plain javascript :)
data.table[2].id // 3
data.table[2].name // "Polly"
table is an immediate child of data, and this gets it's third child (arrays are 0 based).
The alternative, if I misunderstood and you want to search by id, would be something like this:
for(var i in data.table) {
var o = data.table[i];
if(o.id == 3) alert(o.name); // "Polly"
}

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