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Object transformation using a functional approach

I am reading a simple data set from a data.txt file. I would like to take this data and transform it into a specific object as per my example below. I have managed to get it into a somewhat usable JSON object but this is not ideal. I have included an example of the desired object.
Here is my app.js file:
let output = fs.readFileSync('./data.txt', 'UTF8')
.trim()
.split('\r\n')
.map((line) => line.split(';'))
.reduce((customers, line) => {
customers.push({
name: line[0],
product: [{
item: line[1],
serial: line[2],
year: line[3]
}]
})
return customers
}, [])
console.log(JSON.stringify(output, null, 2))
This currently the above NodeJs code returns the following array object:
[
{
"name": "Nancy",
"product": [
{
"item": "Macbook Pro",
"serial": "A34D05980FCD4303",
"year": "2019"
}
]
},
{
"name": "Nancy",
"product": [
{
"item": "iPad",
"serial": "O0403X3028423C92",
"year": "2015"
}
]
},
{
"name": "Nancy",
"product": [
{
"item": "iPhone",
"serial": "X3830238S3309230",
"year": "2017"
}
]
},
{
"name": "John",
"product": [
{
"item": "Macbook Pro",
"serial": "X2020J393983H380",
"year": "2013"
}
]
},
{
"name": "John",
"product": [
{
"item": "iPhone",
"serial": "X38320093X032309",
"year": "2015"
}
]
},
{
"name": "fluffikins",
"product": [
{
"item": "iMac",
"serial": "F392D392033X3232",
"year": "2013"
}
]
},
{
"name": "fluffikins",
"product": [
{
"item": "iPad",
"serial": "FE322230D3223S21",
"year": "2011"
}
]
}
]
What I am trying to do is get the below object returned - ideally still following the same functional approach:
[
{
"name": "Nancy",
"product": [
{
"item": "Macbook Pro",
"serial": "A34D05980FCD4303",
"year": "2019"
},
{
"item": "iPad",
"serial": "O0403X3028423C92",
"year": "2015"
},
{
"item": "iPhone",
"serial": "X3830238S3309230",
"year": "2017"
}
]
},
{
"name": "John",
"product": [
{
"item": "Macbook Pro",
"serial": "X2020J393983H380",
"year": "2013"
},
{
"item": "iPhone",
"serial": "X38320093X032309",
"year": "2015"
}
]
},
{
"name": "fluffikins",
"product": [
{
"item": "iMac",
"serial": "F392D392033X3232",
"year": "2013"
},
{
"item": "iPad",
"serial": "FE322230D3223S21",
"year": "2011"
}
]
}
]
Here is my mock data set that lives in data.txt
Nancy;Macbook Pro;A34D05980FCD4303;2019
Nancy;iPad;O0403X3028423C92;2015
Nancy;iPhone;X3830238S3309230;2017
John;Macbook Pro;X2020J393983H380;2013
John;iPhone;X38320093X032309;2015
fluffikins;iMac;F392D392033X3232;2013
fluffikins;iPad;FE322230D3223S21;2011

Instead of an array you can use Map in reduce as accumulator, use name as key in Map and club value of all keys, finally just get the values Map to get desired output
const data = `Nancy;Macbook Pro;A34D05980FCD4303;2019
Nancy;iPad;O0403X3028423C92;2015
Nancy;iPhone;X3830238S3309230;2017
John;Macbook Pro;X2020J393983H380;2013
John;iPhone;X38320093X032309;2015
fluffikins;iMac;F392D392033X3232;2013
fluffikins;iPad;FE322230D3223S21;2011`
const final = data.split('\n')
.map(v => v.split(';'))
.reduce((op, [name, item, serial, year]) => {
let obj = { item, serial, year }
if (op.has(name)) {
op.get(name).products.push(obj)
} else{
op.set(name,{name, products:[obj]})
}
return op
}, new Map())
console.log([...final.values()])

Here is a "functional version" that utilizes a Map to find duplicates in O(1):
(map => (
fs.readFileSync('./data.txt', 'UTF8')
.trim()
.split('\r\n')
.map((line) => line.split(';'))
.forEach(([name, item, serial, year]) =>
map.has(name)
? map.get(name).product.push({ item, serial, year })
: map.set(name, { name, product: [{ item, serial, year }] })
),
[...map.values()]
)(new Map)
But seriously, whats so bad about imperative style?:
const customers = new Map;
const entries = fs.readFileSync('./data.txt', 'UTF8')
.trim()
.split('\r\n');
for(const entry of entries) {
const [name, item, serial, year] = entry.split(";");
const product = { item, serial, year };
if(customers.has(name)) {
customers.get(name).product.push(product);
} else customers.set(name, { name, product: [product] });
}
const result = [...customers.values()];

You can modify the .reduce function to only add a new item to the array if there isn't one with that name. If there is, just add the product to that item's product array.
const data = `Nancy;Macbook Pro;A34D05980FCD4303;2019
Nancy;iPad;O0403X3028423C92;2015
Nancy;iPhone;X3830238S3309230;2017
John;Macbook Pro;X2020J393983H380;2013
John;iPhone;X38320093X032309;2015
fluffikins;iMac;F392D392033X3232;2013
fluffikins;iPad;FE322230D3223S21;2011`;
const result = data.trim()
.split('\n')
.map((line) => line.split(';'))
.reduce((customers, line) => {
const product = {
item: line[1],
serial: line[2],
year: line[3]
};
const customer = customers.find(({
name
}) => name === line[0]);
if (customer) {
customer.product.push(product);
} else {
customers.push({
name: line[0],
product: [product]
});
}
return customers
}, []);
console.log(result);

How to insert a row in Javascript with a loop?

I have a json file and I want to convert the data into a table with Javascript. I found some similar questions How to convert the following table to JSON with javascript? , loop through a json object, but they all use jQuery and show the table on html web. I just need a simple loop to insert row into the table. I tried 'append', 'insert' and 'insertRow', all not work. Could anyone give me a hint?
Json file:
{
"name": "lily",
"country": "china",
"age": 23
},
{
"name": "mike",
"country": "japan",
"age": 22
},
{
"name": "lucy",
"country": "korea",
"age": 25
}
My code:
var jdata = {};
jdata.cols = [
{
"id": "1",
"label": "name",
"type": "string"
},
{
"id": "2",
"label": "country",
"type":"string"
}
];
for(var i = 1; i < 3; i++){
row = [
{
"c": [
{
"v": json["hits"]["hits"][i]["_source"]["name"]
},
{
"v": json["hits"]["hits"][i]["_source"]["country"]
}
]
}
];
jdata.rows.insertRow(row);
}
Edit: Add expected output: change the json file to the following structure.
[
['lily', 'china'],
['mike', 'japan'],
['lucy', 'korea'],
]

I guess you need push (Or concat / push(...elements) if you want to add array of rows)
jdata.rows = [];
for(var i = 1; i < 3; i++){
row = [
{
"c": [
{
"v": json["hits"]["hits"][i]["_source"]["name"]
},
{
"v": json["hits"]["hits"][i]["_source"]["country"]
}
]
}
];
jdata.rows.push(row);
// for elements from row
// jdata.rows.push(...row)
}

There are a few errors in your code
The JSON needs to be an array so you can loop through each object to display.
insertRow() is a method from the Table object, jdata.rows is not a Table object but an array.
Since, you have used insertRow(), I have rewritten your code to display the table data using the Table Object methods. Here is a code snippet
Edit: You can use the push() method to create your required JSON structure. I have edited the code snippet to create your required JSON.
var jdata = {
cols: [{
"id": "1",
"label": "name",
"type": "string"
},
{
"id": "2",
"label": "country",
"type": "string"
}
],
rows: []
};
var persons = [{
"name": "lily",
"country": "china",
"age": 23
},
{
"name": "mike",
"country": "japan",
"age": 22
}, {
"name": "lucy",
"country": "korea",
"age": 25
}
];
var table = document.getElementById("table");
var header = table.createTHead();
var footer = table.createTFoot();
var rowHeader = header.insertRow(0);
jdata.cols.forEach((col, index) => {
var cell = rowHeader.insertCell(index);
cell.innerHTML = col.label;
});
persons.forEach((person, index) => {
var rowFooter = footer.insertRow(index);
rowFooter.insertCell(0).innerHTML = person.name;
rowFooter.insertCell(1).innerHTML = person.country;
jdata.rows.push([person.name, person.country]);
});
console.log(jdata.rows);
<table id="table">
</table>

What is the most performant way to convert an Array of Object to an Object with unique keys

I am trying to figure out the most performant Javascript way to convert an array of objects, into an object with unique keys and an array full of objects as the value.
For Example:
const array = [
{ "name": "greg", "year": "2000" },
{ "name": "john", "year": "2002" },
{ "name": "bob", "year": "2005" },
{ "name": "ned", "year": "2000" },
{ "name": "pam", "year": "2000" },
];
I would like this converted to:
{
"2000": [
{ "name": "greg", "year": "2000" },
{ "name": "ned", "year": "2000" },
{ "name": "pam", "year": "2000" }
],
"2002": [ { "name": "john", "year": "2002" } ],
"2005": [ { "name": "bob", "year": "2005" } ],
}
As of now, this is what I've done so far:
let yearsObj = {};
for (let i=0; i<array.length; i++) {
if (!yearsObj[array[i].year]) {
yearsObj[array[i].year] = [];
}
yearsObj[array[i].year].push(array[i]);
}

you can use a more elegant way to do it by using array's reduce function
// # impl
const group = key => array =>
array.reduce(
(objectsByKeyValue, obj) => ({
...objectsByKeyValue,
[obj[key]]: (objectsByKeyValue[obj[key]] || []).concat(obj)
}),
{}
);
// # usage
console.log(
JSON.stringify({
byYear: group(array),
}, null, 1)
);
// output
VM278:1 {
"carsByBrand": {
"2000": [
{
"name": "greg",
"year": "2000"
},
{
"name": "ned",
"year": "2000"
},
{
"name": "pam",
"year": "2000"
}
],
"2002": [
{
"name": "john",
"year": "2002"
}
],
"2005": [
{
"name": "bob",
"year": "2005"
}
]
}
}

It could be as simple as that Object.fromEntries(array.map(obj => [obj.year,obj])) even it is not exactly what you need, but talking about performance it is way slower than all proposed, so i'm giving it as an bad example of showing how the short statement is not always the fastest.
Your way seems to be the fastest taking about performance.
Run the snippet below to see the actual timing.
// common
let array = [
{ "name": "greg", "year": "2000" },
{ "name": "john", "year": "2002" },
{ "name": "bob", "year": "2005" },
{ "name": "ned", "year": "2000" },
{ "name": "pam", "year": "2000" },
];
// simple as a statement way
console.time();
console.log(Object.fromEntries(array.map(obj => [obj.year,obj])));
console.timeEnd();
// using .reduce way
console.time();
const result = array.reduce((prev, curr) => {
const { year } = curr;
if (prev[year]) {
prev[year].push(curr);
} else {
prev[year] = [curr];
}
return prev;
}, {});
console.log(result);
console.timeEnd();
// your way
console.time();
let yearsObj = {};
for (let i=0; i<array.length; i++) {
if (!yearsObj[array[i].year]) {
yearsObj[array[i].year] = [];
}
yearsObj[array[i].year].push(array[i]);
}
console.log(yearsObj);
console.timeEnd();

A for loop (imperative style) like you have is likely to be the fastest in most situations. However, in this case you are not likely to see much of a difference. One thing you could do to improve the code in your example is to get the array length before the for loop and assign it to the variable, so that it's not calculated every iteration of the loop.
const yearsObj = {};
const arrayLength = array.length; // Only calculate array length once
for (let i=0; i<arrayLength; i++) {
if (!yearsObj[array[i].year]) {
yearsObj[array[i].year] = [];
}
yearsObj[array[i].year].push(array[i]);
}
In this situation, my preference would be to use Array.reduce(). It is more readable and the performance difference will be negligible.
const arr = [
{ name: 'greg', year: '2000' },
{ name: 'john', year: '2002' },
{ name: 'bob', year: '2005' },
{ name: 'ned', year: '2000' },
{ name: 'pam', year: '2000' },
];
const result = arr.reduce((prev, curr) => {
const { year } = curr;
if (prev[year]) {
prev[year].push(curr);
} else {
prev[year] = [curr];
}
return prev;
}, {});
/* Result:
{ '2000':
[ { name: 'greg', year: '2000' },
{ name: 'ned', year: '2000' },
{ name: 'pam', year: '2000' } ],
'2002': [ { name: 'john', year: '2002' } ],
'2005': [ { name: 'bob', year: '2005' } ] }
*/

Create new array with another structure in Javascript

I want to create a new array based on an original array but with merged data.
Every name key need to have merged date+time (format: YYYY-MM-DD HH:MM) with merged scores. All unique datetimes need to be available as key for each name.
ARRAY ORIGINAL:
"data": [{
"name": "A",
"history": [{
"created": "2017-05-16 00:00:00",
"score": "1"
},
{
"created": "2017-05-16 00:01:10",
"score": "1"
},
{
"created": "2017-05-16 00:01:30",
"score": "1"
}
]
},
{
"name": "B",
"history": [{
"created": "2017-05-16 00:01:00",
"score": "1"
}]
}
]
ARRAY THAT I WANT:
{
[A]: {
"2017-05-16 00:00": 1,
"2017-05-16 00:01": 2
},
[B]: {
"2017-05-16 00:00": 0,
"2017-05-16 00:01": 1
}
}
I hope you guys can help me out. I can't even think of an efficiënt way to do this, unfortunately. I tried to solve this issue with 5 foreach statements with no luck :(

You could use two arrays for names and times as closure and generate for all names and times a property with zero value.
var data = { data: [{ name: "A", history: [{ created: "2017-05-16 00:00:00", score: "1" }, { created: "2017-05-16 00:01:10", score: "1" }, { created: "2017-05-16 00:01:30", score: "1" }] }, { name: "B", history: [{ created: "2017-05-16 00:01:00", score: "1" }] }] },
result = data.data.reduce(function (names, times) {
return function (r, a) {
if (!r[a.name]) {
r[a.name] = {};
times.forEach(function (time) {
r[a.name][time] = 0;
});
names.push(a.name);
}
a.history.forEach(function (o) {
var time = o.created.slice(0, 16);
if (times.indexOf(time) === -1) {
names.forEach(function (name) {
r[name][time] = 0;
});
times.push(time);
}
r[a.name][time] += +o.score;
});
return r;
};
}([], []), {});
console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

You have to create an object not an array, As arrays cannot have a key-value pair in javascript. There is no associative array concept in javascript. You have to use objects in javascript for that.
Here is how you can do what you are trying to achieve using objects.
value = {
"data": [{
"name": "A",
"history": [{
"created": "2017-05-16 00:00:00",
"score": "1"
},
{
"created": "2017-05-16 00:01:10",
"score": "1"
},
{
"created": "2017-05-16 00:01:30",
"score": "1"
}
]},
{
"name": "B",
"history": [{
"created": "2017-05-16 00:01:00",
"score": "1"
}]
}]
};
var result ={};
value.data.forEach(function(v){
var score = {};
for(var i=0;i<v.history.length;i++){
score[v.history[i].created] = v.history[i].score;
}
result[v.name] = score;
});
console.log(result);
Now you can access data as result.A or result[A] and result.B or result[B]
SNIPPET
value = {
"data": [{
"name": "A",
"history": [{
"created": "2017-05-16 00:00:00",
"score": "1"
},
{
"created": "2017-05-16 00:01:10",
"score": "1"
},
{
"created": "2017-05-16 00:01:30",
"score": "1"
}
]
},
{
"name": "B",
"history": [{
"created": "2017-05-16 00:01:00",
"score": "1"
}]
}
]
};
var result = {};
value.data.forEach(function(v) {
var score = {};
for (var i = 0; i < v.history.length; i++) {
score[v.history[i].created] = v.history[i].score;
}
result[v.name] = score;
});
console.log(result);

JavaScript multi-level sorting with multi dimension array

I have a JSON object like below:
[
{
"name": "Robert",
"age":32,
"country": "UK"
},
{
"name": "Prasad",
"age":28,
"country": "India"
},
{
"name": "Benny",
"age":45,
"country": "USA"
},
{
"name": "Robin",
"age":34,
"country": "UK"
},
{
"name": "Bob",
"age":20,
"country": "India"
}
]
I have applied the array sorting for "name" column alone. I want to apply sort for “name” column first and then “age”.
This is how i sort the array by name:
var sort_by = function(field, reverse, primer){
var key = primer ?
function(x) {return primer(x[field])} :
function(x) {return x[field]};
reverse = [-1, 1][+!!reverse];
return function (a, b) {
return a = key(a), b = key(b), reverse * ((a > b) - (b > a));
}
}
Call the sort function:
arrayToSort.sort(
sort_by( “name”, true, function(a){
return a.toUpperCase();
}) );
How can I get the array sorted like below?
[{
"name": "Bob",
"age":20,
"country": "India"
},
{
"name": "Benny",
"age":45,
"country": "USA"
},
{
"name": "Prasad",
"age":28,
"country": "India"
},
{
"name": "Robert",
"age":32,
"country": "UK"
},
{
"name": "Robin",
"age":34,
"country": "UK"
}]

I think what you are looking for is a way to "chain" sort_by(..) calls so as to be able to operate on more than one field.
Below is a slightly modified version of your code. Its pretty much self-explanatory.
arrayToSort = [ ...];
var sort_by = function(field, reverse, primer){
var key = primer ?
function(x) {return primer(x[field]); }:
function(x) {return x[field] };
reverse = [-1, 1][+!!reverse];
return function (a, b) {
a = key(a);
b = key(b);
return a==b ? 0 : reverse * ((a > b) - (b > a));
//^ Return a zero if the two fields are equal!
}
}
var chainSortBy = function(sortByArr) {
return function(a, b) {
for (var i=0; i<sortByArr.length; i++) {
var res = sortByArr[i](a,b);
if (res != 0)
return res; //If the individual sort_by returns a non-zero,
//we found inequality, return the value from the comparator.
}
return 0;
}
}
arrayToSort.sort(
chainSortBy([
sort_by( "name", true, function(a){
return a.toUpperCase();
}),
sort_by("age", true, null)
])
);
console.log(arrayToSort); //Check browser console.
For output: check the JSFiddle

The solution is back to native, just :
function orderByProp(arr,prop){
var order = [], ordered=[];
//create temp ID and Save the real index
for(i=0; i < arr.length;++i){ order.push(arr[i][prop]+"-:-"+i);}
ordered.sort();
for(i=0; i < arr.length;++i){
var val = order.split("-:-");
ordered.push(arr[val[1]]); Get the real array by saved index
}
return ordered;
}
// Apply
var arr = [{
"name": "Bob",
"age":20,
"country": "India"
},
{
"name": "Benny",
"age":45,
"country": "USA"
},
{
"name": "Prasad",
"age":28,
"country": "India"
},
{
"name": "Robert",
"age":32,
"country": "UK"
},
{
"name": "Robin",
"age":34,
"country": "UK"
}];
var sort = orderByProp(arr,"name");
i'm not tested this. but hope it could solve your problems

This is relatively trivial with the Array.sort method by using the || operator, where it will use the second value if the first comparison returns 0, meaning the value was the same:
const data = [
{
"name": "Robert",
"age": 32,
},
{
"name": "David",
"age": 24,
},
{
"name": "Robert",
"age": 28,
},
];
const sortedData = data.sort((a, b) => a.name.localeCompare(b.name) || a.age - b.age);
console.log(sortedData);
Credit for this goes to #NinaScholz for her answer here.