Objects and Associative Arrays
Objects, JSON, AssociativeArrays, Maps and Sets
SoftUni Team
Technical Trainers
Software University
Table of Contents
1.Objects and JSON
2.Associative Arrays
3.The Map Class
4.The Set Class
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3
sli.do#9835
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Objects in JS
Objects, Properties and JSON
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Objects in JavaScript hold key-value pairs:
Objects in JS
let obj = { name : "SoftUni", age : 3 };let obj = { name : "SoftUni", age : 3 };
console.log(obj); // Object {name: "SoftUni", age: 3}console.log(obj); // Object {name: "SoftUni", age: 3}
obj['site'] = "https://softuni.bg";obj['site'] = "https://softuni.bg";
obj.age = 10;obj.age = 10;
obj["name"] = "Software University";obj["name"] = "Software University";
console.log(obj); // Object {name: "Software University", age: 10,site: "https://softuni.bg"}console.log(obj); // Object {name: "Software University", age: 10,site: "https://softuni.bg"}
delete obj.name; // Delete a propertydelete obj.name; // Delete a property
obj.site = undefined; // Delete a property valueobj.site = undefined; // Delete a property value
console.log(obj); // Object {age: 10, site: undefined}console.log(obj); // Object {age: 10, site: undefined}
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More about Objects
let sofia =let sofia =
{ name: "Sofia", lat: 42.696552, long: 23.326011 }; { name: "Sofia", lat: 42.696552, long: 23.326011 };
console.log(Object.keys(sofia)); // ["name", "lat", "long"]console.log(Object.keys(sofia)); // ["name", "lat", "long"]
let emptyObj = { };let emptyObj = { };
console.log(Object.keys(emptyObj)); // []console.log(Object.keys(emptyObj)); // []
console.log(Object.hasOwnProperty('name')); // trueconsole.log(Object.hasOwnProperty('name')); // true
if (sofia.age === undefined)if (sofia.age === undefined)
console.log("Key 'age' does not exist"); console.log("Key 'age' does not exist");
if (sofia.name !== undefined)if (sofia.name !== undefined)
console.log("Key 'name' exists"); console.log("Key 'name' exists");
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JavaScript objects can be stored as text in JSON format
Objects and JSON
let obj = { name : "SoftUni", age : 3 };let obj = { name : "SoftUni", age : 3 };
let str = JSON.stringify(obj);let str = JSON.stringify(obj);
console.log(str); // {"name":"SoftUni","age":3}console.log(str); // {"name":"SoftUni","age":3}
let str = "{\"name\":\"Nakov\",\"age\":24}"let str = "{\"name\":\"Nakov\",\"age\":24}"
let obj = JSON.parse(str);let obj = JSON.parse(str);
console.log(obj); // Object {name: "Nakov", age: 24}console.log(obj); // Object {name: "Nakov", age: 24}
Read an array of strings, holding towns with GPS coordinates
Parse each string to JS object (see the below format)
Print the output array of objects as JSON string
8
Problem: Towns to JSON
[{"Town":"Sofia","Latitude":42.696552,"Longitude":23.32601},{"Town":"Beijing","Latitude":39.913818,"Longitude":116.363625}][{"Town":"Sofia","Latitude":42.696552,"Longitude":23.32601},{"Town":"Beijing","Latitude":39.913818,"Longitude":116.363625}]
| Town | Latitude | Longitude || Town | Latitude | Longitude |
| Sofia | 42.696552 | 23.32601 || Sofia | 42.696552 | 23.32601 |
| Beijing | 39.913818 | 116.363625 || Beijing | 39.913818 | 116.363625 |
9
Solution: Towns to JSON
Check your solution here: https://judge.softuni.bg/Contests/315
function parseTownsToJSON(towns) {function parseTownsToJSON(towns) {
let townsArr = []; let townsArr = [];
for (let town of towns.slice(1)) { for (let town of towns.slice(1)) {
let [empty, townName, lat, lng] = let [empty, townName, lat, lng] =
town.split(/\s*\|\s*/); town.split(/\s*\|\s*/);
let townObj = { Town: townName, Latitude: let townObj = { Town: townName, Latitude:
Number(lat), Longitude: Number(lng) }; Number(lat), Longitude: Number(lng) };
townsArr.push(townObj); townsArr.push(townObj);
} }
return JSON.stringify(townsArr); return JSON.stringify(townsArr);
}}
parseTownsToJSON(['|Town|Lat|Lng|', '|Sofia |42|23|'])parseTownsToJSON(['|Town|Lat|Lng|', '|Sofia |42|23|'])
10
Nested Objects in JS
let polygon = {let polygon = {
about: { name: "triangle", color: "red" }, about: { name: "triangle", color: "red" },
corners: [{x:2, y:6}, {x:3, y:1}, {x:-2, y:2}] corners: [{x:2, y:6}, {x:3, y:1}, {x:-2, y:2}]
};};
console.log(JSON.stringify(polygon)); //{"about":{"name":"triangle","color":"red"},"corners":[{"x":2,"y":6},{"x":3,"y":1},{"x":-2,"y":2}]}console.log(JSON.stringify(polygon)); //{"about":{"name":"triangle","color":"red"},"corners":[{"x":2,"y":6},{"x":3,"y":1},{"x":-2,"y":2}]}
console.log(polygon.about.color); // redconsole.log(polygon.about.color); // red
polygon.about.location = {x:4, y:-7};polygon.about.location = {x:4, y:-7};
Problem: Score to HTML
Read a JSON string, holding array of objects: {name, score}
Print the objects as HTML table like shown below
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<table><table>
<tr><th>name</th><th>score</th><tr> <tr><th>name</th><th>score</th><tr>
<tr><td>Pesho & Kiro</td><td>479</td></tr> <tr><td>Pesho & Kiro</td><td>479</td></tr>
<tr><td>Gosho, Maria & Viki</td><td>205</td></tr> <tr><td>Gosho, Maria & Viki</td><td>205</td></tr>
</table></table>
[{"name":"Pesho & Kiro","score":479},{"name":"Gosho,Maria & Viki","score":205}][{"name":"Pesho & Kiro","score":479},{"name":"Gosho,Maria & Viki","score":205}]
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Solution: Score to HTML
Check your solution here: https://judge.softuni.bg/Contests/315
function scoreToHTMLTable([scoreJSON]) {function scoreToHTMLTable([scoreJSON]) {
let html = "<table>\n"; let html = "<table>\n";
html += " <tr><th>name</th><th>score</th>\n"; html += " <tr><th>name</th><th>score</th>\n";
let arr = JSON.parse(scoreJSON); let arr = JSON.parse(scoreJSON);
for (let obj of arr) for (let obj of arr)
html += ` <tr><td>${htmlEscape(obj['name'])}` + html += ` <tr><td>${htmlEscape(obj['name'])}` +
`</td><td>${obj['score']}</td></tr>\n`; `</td><td>${obj['score']}</td></tr>\n`;
return html + "</table>"; return html + "</table>";
function htmlEscape(text) { // TODO … } function htmlEscape(text) { // TODO … }
}}
scoreToHTMLTable(['[{"name":"Pesho","score":70}]'])scoreToHTMLTable(['[{"name":"Pesho","score":70}]'])
Read a JSON string, holding array of JS objects (key / value pairs)
Print the objects as HTML table like shown below
13
Problem: From JSON to HTML Table
<table><table>
<tr><th>Name</th><th>Price</th></tr> <tr><th>Name</th><th>Price</th></tr>
<tr><td>Tomatoes & Chips</td><td>2.35</td></tr> <tr><td>Tomatoes & Chips</td><td>2.35</td></tr>
<tr><td>J&B Chocolate</td><td>0.96</td></tr> <tr><td>J&B Chocolate</td><td>0.96</td></tr>
</table></table>
[{"Name":"Tomatoes & Chips","Price":2.35},{"Name":"J&BChocolate","Price":0.96}][{"Name":"Tomatoes & Chips","Price":2.35},{"Name":"J&BChocolate","Price":0.96}]
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Solution: From JSON to HTML Table
Check your solution here: https://judge.softuni.bg/Contests/315
function JSONToHTMLTable([json]) {function JSONToHTMLTable([json]) {
let html = "<table>\n"; let html = "<table>\n";
let arr = JSON.parse(json); let arr = JSON.parse(json);
html += " <tr>"; html += " <tr>";
for (let key of Object.keys(arr[0])) for (let key of Object.keys(arr[0]))
html += `<th>${htmlEscape(key)}</th>`; html += `<th>${htmlEscape(key)}</th>`;
html += "</tr>\n"; html += "</tr>\n";
for (let obj of arr) { for (let obj of arr) {
// TODO: print obj values in <tr><td>…</td></tr> // TODO: print obj values in <tr><td>…</td></tr>
return html + "</table>"; return html + "</table>";
function htmlEscape(text) { // TODO … } function htmlEscape(text) { // TODO … }
}}
JSONToHTMLTable(['[{"X":5,"Y":7},{"X":2,"Y":4}]'])JSONToHTMLTable(['[{"X":5,"Y":7},{"X":2,"Y":4}]'])
Associative Arrays
Objects as Associative Arrays in JS
John SmithJohn Smith
+1-555-8976+1-555-8976
NakovNakov
+359-2-981-9819+359-2-981-9819
Sam DoeSam Doe
+1-555-5030+1-555-5030
key
value
Associative arrays (maps / dictionaries) == arrays indexed by keys
Not by the numbers 0, 1, 2, …
Hold a set of pairs {key value}, just like JS objects
Associative Arrays (Maps, Dictionaries)
Associative array (dictionary)
John SmithJohn Smith
+1-555-8976+1-555-8976
Lisa SmithLisa Smith
+1-555-1234+1-555-1234
Sam DoeSam Doe
+1-555-5030+1-555-5030
key
value
Traditional array
0 1 2 3 40 1 2 3 4
88
-3-3
1212
408408
3333
key
value
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Phonebook – Associative Array Example
let phonebook = { };let phonebook = { };
phonebook["John Smith"] = "+1-555-8976"; // Addphonebook["John Smith"] = "+1-555-8976"; // Add
phonebook["Lisa Smith"] = "+1-555-1234";phonebook["Lisa Smith"] = "+1-555-1234";
phonebook["Sam Doe"] = "+1-555-5030";phonebook["Sam Doe"] = "+1-555-5030";
phonebook["Nakov"] = "+359-899-555-592";phonebook["Nakov"] = "+359-899-555-592";
phonebook["Nakov"] = "+359-2-981-9819"; // Replacephonebook["Nakov"] = "+359-2-981-9819"; // Replace
delete phonebook["John Smith"]; // Deletedelete phonebook["John Smith"]; // Delete
console.log(Object.keys(phonebook).length); // 3console.log(Object.keys(phonebook).length); // 3
for (let key in phonebook) // Printfor (let key in phonebook) // Print
console.log(`${key} -> ${phonebook[key]}`); console.log(`${key} -> ${phonebook[key]}`);
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The order of keys in JS objects is unspecified!
The Order of Keys in JS Object
let obj = {let obj = {
"1": 'one', "1": 'one',
"3": 'three', "3": 'three',
"2": 'two', "2": 'two',
"z": 'z', "z": 'z',
"a": 'a' "a": 'a'
}}
console.log(Object.keys(obj)); // ["1", "2", "3", "z", "a"]console.log(Object.keys(obj)); // ["1", "2", "3", "z", "a"]
console.log(obj); // Object {1: "one", 2: "two", 3: "three", z:"z", a: "a"}console.log(obj); // Object {1: "one", 2: "two", 3: "three", z:"z", a: "a"}
Read towns and incomes (like shown below) and print a JSONobject holding the total income for each town (see below)
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Problem: Sum by Town
{"Sofia":"25","Varna":"7"}{"Sofia":"25","Varna":"7"}
SofiaSofia
2020
VarnaVarna
33
SofiaSofia
55
VarnaVarna
44
Print the towns in their natural order asobject properties
20
Solution: Sum of Towns
Check your solution here: https://judge.softuni.bg/Contests/315
function sumOfTowns(arr) {function sumOfTowns(arr) {
let sums = {}; let sums = {};
for (let i=0; i<arr.length; i+=2) { for (let i=0; i<arr.length; i+=2) {
let [town, income] = [arr[i], Number(arr[i+1])]; let [town, income] = [arr[i], Number(arr[i+1])];
if (sums[town] == undefined) if (sums[town] == undefined)
sums[town] = income; sums[town] = income;
else else
sums[town] += income; sums[town] += income;
} }
return JSON.stringify(sums); return JSON.stringify(sums);
}}
sumOfTowns(['Sofia','20', 'Varna','10', 'Sofia','5'])sumOfTowns(['Sofia','20', 'Varna','10', 'Sofia','5'])
21
Write a JS function to count the words in a text (case sensitive)
Words are sequences of letters, digits and _
The input text comes as array of strings
Return the output as JSON string
Problem: Count Words in a Text
JS devs use Node.js for server-side JS.JS devs use Node.js for server-side JS.
-- JS for devs-- JS for devs
{"JS":3,"devs":2,"use":1,"Node":1,"js":1,"for":2,"server":1,"side":1}{"JS":3,"devs":2,"use":1,"Node":1,"js":1,"for":2,"server":1,"side":1}
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Solution: Count Words in a Text
Check your solution here: https://judge.softuni.bg/Contests/315
function countWords(inputLines) {function countWords(inputLines) {
let text = inputLines.join('\n'); let text = inputLines.join('\n');
let words = text.split(/[^A-Za-z0-9_]+/) let words = text.split(/[^A-Za-z0-9_]+/)
.filter(w => w != ''); .filter(w => w != '');
let wordsCount = {}; let wordsCount = {};
for (let w of words) for (let w of words)
wordsCount[w] ? wordsCount[w]++ : wordsCount[w] ? wordsCount[w]++ :
wordsCount[w] = 1; wordsCount[w] = 1;
return JSON.stringify(wordsCount); return JSON.stringify(wordsCount);
}}
countWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])countWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])
The Map Class in JS
Key / Value Map
John SmithJohn Smith
+1-555-8976+1-555-8976
NakovNakov
+359-2-981-9819+359-2-981-9819
Sam DoeSam Doe
+1-555-5030+1-555-5030
key
value
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The Map class holds{ key value } map
Better functionality thanplain JS object
The Map Class in JS
let score = new Map();let score = new Map();
score.set("Peter", 130);score.set("Peter", 130);
score.set("Maria", 85);score.set("Maria", 85);
for (let [k, v] of score)for (let [k, v] of score)
console.log(k + ' -> ' + v); console.log(k + ' -> ' + v);
Phonebook – Map Example
let phonebook = new Map();let phonebook = new Map();
phonebook.set("John Smith", "+1-555-8976"); // Addphonebook.set("John Smith", "+1-555-8976"); // Add
phonebook.set("Lisa Smith","+1-555-1234");phonebook.set("Lisa Smith","+1-555-1234");
phonebook.set("Sam Doe", "+1-555-5030");phonebook.set("Sam Doe", "+1-555-5030");
phonebook.set("Nakov", "+359-899-555-592");phonebook.set("Nakov", "+359-899-555-592");
phonebook.set("Nakov", "+359-2-981-9819"); // Replacephonebook.set("Nakov", "+359-2-981-9819"); // Replace
phonebook.delete("John Smith"); // Deletephonebook.delete("John Smith"); // Delete
console.log(phonebook.size); // 3console.log(phonebook.size); // 3
for (let [key, value] of phonebook) // Printfor (let [key, value] of phonebook) // Print
console.log(`${key} -> ${value}`); console.log(`${key} -> ${value}`);
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26
Maps Preserve the Insertion Order of Keys
let map = new Map([let map = new Map([
["1", 'one'], ["1", 'one'],
["3", 'three'], ["3", 'three'],
["2", 'two'], ["2", 'two'],
["z", 'z'], ["z", 'z'],
["a", 'a'] ["a", 'a']
]);]);
console.log(map); // Map {"1" => "one", "3" => "three", "2" =>"two", "z" => "z", "a" => "a"}console.log(map); // Map {"1" => "one", "3" => "three", "2" =>"two", "z" => "z", "a" => "a"}
console.log(Array.from(map.keys()));console.log(Array.from(map.keys()));
// ["1", "3", "2", "z", "a"]// ["1", "3", "2", "z", "a"]
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Write a JS function to count the words in a text (case insensitive)
Words are sequences of letters, digits and _
The input comes as array of strings
Order alphabetically the output words
Problem: Count Words in a Text (with Map)
JS devs use Node.js forserver-side JS.JS devs use Node.js forserver-side JS.
JS devs use JS.JS devs use JS.
-- JS for devs ---- JS for devs --
'devs' -> 3 times'devs' -> 3 times
'for' -> 2 times'for' -> 2 times
'js' -> 6 times'js' -> 6 times
'node' -> 1 times'node' -> 1 times
'server' -> 1 times'server' -> 1 times
'side' -> 1 times'side' -> 1 times
'use' -> 2 times'use' -> 2 times
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Solution: Count Words in a Text (with Map)
Check your solution here: https://judge.softuni.bg/Contests/315
function countWords(inputLines) {function countWords(inputLines) {
let words = inputLines.join('\n').toLowerCase() let words = inputLines.join('\n').toLowerCase()
.split(/[^A-Za-z0-9_]+/).filter(w => w != ''); .split(/[^A-Za-z0-9_]+/).filter(w => w != '');
let wordsCount = new Map(); let wordsCount = new Map();
for (let w of words) for (let w of words)
wordsCount.has(w) ? wordsCount.set(w, wordsCount.has(w) ? wordsCount.set(w,
wordsCount.get(w)+1) : wordsCount.set(w, 1); wordsCount.get(w)+1) : wordsCount.set(w, 1);
let allWords = Array.from(wordsCount.keys()).sort(); let allWords = Array.from(wordsCount.keys()).sort();
allWords.forEach(w => allWords.forEach(w =>
console.log(`'${w}' -> ${wordsCount.get(w)} times`)); console.log(`'${w}' -> ${wordsCount.get(w)} times`));
}}
countWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])countWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])
Read towns and population (like shown below) and print a thetowns and their total population for each town (see below)
Print the towns in the order of their first appearance
29
Problem: Population in Towns
Varna <-> 40000Varna <-> 40000
Sofia <-> 1200000Sofia <-> 1200000
Plovdiv <-> 20000Plovdiv <-> 20000
Sofia <-> 100000Sofia <-> 100000
Varna <-> 420000Varna <-> 420000
Plovdiv <-> 400000Plovdiv <-> 400000
Plovdiv <-> 50000Plovdiv <-> 50000
Varna : 460000Varna : 460000
Sofia : 1300000Sofia : 1300000
Plovdiv : 470000Plovdiv : 470000
30
Solution: Population in Towns
Check your solution here: https://judge.softuni.bg/Contests/315
function populationInTowns(dataRows) {function populationInTowns(dataRows) {
let total = new Map(); let total = new Map();
for (let dataRow of dataRows) { for (let dataRow of dataRows) {
let [town, population] = dataRow.split(/\s*<->\s*/); let [town, population] = dataRow.split(/\s*<->\s*/);
population = Number(population); population = Number(population);
if (total.has(town)) if (total.has(town))
total.set(town, total.get(town) + population); total.set(town, total.get(town) + population);
else total.set(town, population); else total.set(town, population);
} }
for (let [town, sum] of total) for (let [town, sum] of total)
console.log(town + " : " + sum); console.log(town + " : " + sum);
}}
populationInTowns(['B<->20', 'A<->30', 'B<->5'])populationInTowns(['B<->20', 'A<->30', 'B<->5'])
Read sales data in the following format
Print for each town the sum of incomes for each product
Order the towns and product as they first appear
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Problem: City Markets
Sofia -> Laptops HP -> 200 : 2000Sofia -> Laptops HP -> 200 : 2000
Sofia -> Raspberry -> 200000 : 1500Sofia -> Raspberry -> 200000 : 1500
Montana -> Oranges -> 200000 : 1Montana -> Oranges -> 200000 : 1
Montana -> Cherries -> 1000 : 0.3Montana -> Cherries -> 1000 : 0.3
Sofia -> Audi Q7 -> 200 : 100000Sofia -> Audi Q7 -> 200 : 100000
{town} -> {product} -> {amountOfSales}:{priceForOneUnit}{town} -> {product} -> {amountOfSales}:{priceForOneUnit}
Town - SofiaTown - Sofia
$$$Laptops HP : 400000$$$Laptops HP : 400000
$$$Raspberry : 300000000$$$Raspberry : 300000000
$$$Audi Q7 : 20000000$$$Audi Q7 : 20000000
Town - MontanaTown - Montana
$$$Oranges : 200000$$$Oranges : 200000
$$$Cherries : 4000$$$Cherries : 4000
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Solution: City Markets (Nested Maps)
function cityMarkets(sales) {function cityMarkets(sales) {
let townsWithProducts = new Map(); let townsWithProducts = new Map();
for (let sale of sales) { for (let sale of sales) {
let [town, product, quantityPrice] = sale.split(/\s*->\s*/); let [town, product, quantityPrice] = sale.split(/\s*->\s*/);
let [quantity, price] = quantityPrice.split(/\s*:\s*/); let [quantity, price] = quantityPrice.split(/\s*:\s*/);
if (!townsWithProducts.has(town)) if (!townsWithProducts.has(town))
townsWithProducts.set(town, new Map()); townsWithProducts.set(town, new Map());
let income = quantity * price; let income = quantity * price;
let oldIncome = townsWithProducts.get(town).get(product); let oldIncome = townsWithProducts.get(town).get(product);
if (oldIncome) income += oldIncome; if (oldIncome) income += oldIncome;
townsWithProducts.get(town).set(product, income); townsWithProducts.get(town).set(product, income);
} }
// TODO: print the incomes by towns and products // TODO: print the incomes by towns and products
}}
Check your solution here: https://judge.softuni.bg/Contests/315
The Set Class in JS
Set of Unique Values of Any Type
34
Sets in JS are collections of unique objects
The insertion order is preserved, with no duplicates
The Set Class in JS
let names = new Set();let names = new Set();
names.add("Peter"); names.add(20);names.add("Peter"); names.add(20);
names.add("Maria"); names.add(5);names.add("Maria"); names.add(5);
console.log(names.has('Peter')); // trueconsole.log(names.has('Peter')); // true
names.add("Maria"); // Duplicates are skippednames.add("Maria"); // Duplicates are skipped
names.delete(20); // Delete element if existsnames.delete(20); // Delete element if exists
for (let name of names) console.log(name);for (let name of names) console.log(name);
35
Write a JS function to extract all unique words from a text (caseinsensitive)
Words are sequences of letters, digits and _
The input comes as array of strings
The output should hold the words in their order of appearance
Problem: Extract Unique Words
JS devs use Node.js forserver-side JS.JS devs use Node.js forserver-side JS.
JS devs use JS.JS devs use JS.
-- JS for devs ---- JS for devs --
js, devs, use,node, for, server,sidejs, devs, use,node, for, server,side
36
Solution: Extract Unique Words
Check your solution here: https://judge.softuni.bg/Contests/315
function extractWords(inputSentences) {function extractWords(inputSentences) {
let wordPattern = /\b[a-zA-Z0-9_]+\b/g; let wordPattern = /\b[a-zA-Z0-9_]+\b/g;
let words = new Set(); let words = new Set();
for (let sentence of inputSentences) { for (let sentence of inputSentences) {
let matches = sentence.match(wordPattern); let matches = sentence.match(wordPattern);
matches.forEach(x=>words.add(x.toLowerCase())); matches.forEach(x=>words.add(x.toLowerCase()));
} }
console.log([...words.values()].join(", ")); console.log([...words.values()].join(", "));
}}
extractWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])extractWords(['JS and Node.js', 'JS again and again', 'Oh, JS?'])
Practice: Using Objects, Maps, Sets
Live Exercises in Class (Lab)
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Objects in JS hold key-value pairs
Maps map keys to values, preserve keys order
Sets hold unique collection of values
Summary
let obj = { name : "SoftUni", age : 3 };let obj = { name : "SoftUni", age : 3 };
obj.age++;obj.age++;
obj[town] = 'Sofia';obj[town] = 'Sofia';
delete obj.name;delete obj.name;
let map = new Map();let map = new Map();
map.set('score', 20);map.set('score', 20);
let map = new Set(); set.add(5);let map = new Set(); set.add(5);
License
This course (slides, examples, demos, videos, homework, etc.)is licensed under the "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International" license
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