forEach & filter & map & sort & reduce

 

 

const companies = [
    {name: "Company One", category: "Finance", start: 1981, end: 2003},
    {name: "Company Two", category: "Retail", start: 1992, end: 2008},
    {name: "Company Three", category: "Auto", start: 1999, end: 2007},
    {name: "Company Four", category: "Retail", start: 1985, end: 2010},
    {name: "Company Five", category: "Technology", start: 2009, end: 2017},
    {name: "Company Six", category: "Finance", start: 2000, end: 2015},
    {name: "Company Seven", category: "Auto", start: 1986, end: 1998},
    {name: "Company Eight", category: "Technology", start: 2011, end: 2018},
    {name: "Company Nine", category: "Retail", start: 1980, end: 1989}
];

const ages = [33, 12, 20, 16, 5, 54, 21, 44, 61, 13, 15, 45, 25, 64, 32];

 

 

1. forEach

// basic for
for(let i = 0; i < companies.length; i++){
    console.log(companies[i]);
}

// forEach
companies.forEach(function(company) {
    console.log(company.name);
})

/*
Company One
Company Two
Company Three
Company Four
Company Five
Company Six
Company Seven
Company Eight
Company Nine
*/

 

 

2. filter

const canDrink2 = ages.filter(function(age){
    if(age >= 21){
        return true;
    }
})
console.log(canDrink2);
// [ 33, 54, 21, 44, 61, 45, 25, 64, 32] 

// more clean code
const canDrink3 = ages.filter(age => age >= 21);
console.log(canDrink3);


// Filter retail companies
const retailCompanies = companies.filter(function(company){
    if(company.category === 'Retail'){
        return true;
    }
})
console.log(retailCompanies);
/*
[
  { name: 'Company Two', category: 'Retail', start: 1992, end: 2008 },
  { name: 'Company Four', category: 'Retail', start: 1985, end: 2010 },
  { name: 'Company Nine', category: 'Retail', start: 1980, end: 1989 }
]
*/

// more clean code
const retailCompanies2 = companies.filter(company => company.category === 'Retail');
console.log(retailCompanies2);


// Get 80s companies
const eightiesCompanies = companies.filter(company => (company.start >= 1980 && company.start < 1990));
console.log(eightiesCompanies);
/*
[
  { name: 'Company One', category: 'Finance', start: 1981, end: 2003 },
  { name: 'Company Four', category: 'Retail', start: 1985, end: 2010 },
  { name: 'Company Seven', category: 'Auto', start: 1986, end: 1998 },
  { name: 'Company Nine', category: 'Retail', start: 1980, end: 1989 }
]
*/

// Get companies that lasted 10 years or more
const lastedTenYears = companies.filter(company => (company.end - company.start >= 10));
console.log(lastedTenYears);
/*
[
  { name: 'Company One', category: 'Finance', start: 1981, end: 2003 },
  { name: 'Company Two', category: 'Retail', start: 1992, end: 2008 },
  { name: 'Company Four', category: 'Retail', start: 1985, end: 2010 },
  { name: 'Company Six', category: 'Finance', start: 2000, end: 2015 },
  { name: 'Company Seven', category: 'Auto', start: 1986, end: 1998 }
] 
*/

 

 

3. map

// Create array of company names
const companyNames = companies.map(function(company){
    return company.name;
})
console.log(companyNames);

// more clean code
const companyNames2 = companies.map(company => company.name)
console.log(companyNames2);


const testMap = companies.map(
                        company => 
                        `${company.name} [${company.start} - ${company.end}]`);
console.log(testMap);
/*
[
  'Company One [1981 - 2003]',
  'Company Two [1992 - 2008]',
  'Company Three [1999 - 2007]',
  'Company Four [1985 - 2010]',
  'Company Five [2009 - 2017]',
  'Company Six [2000 - 2015]',
  'Company Seven [1986 - 1998]',
  'Company Eight [2011 - 2018]',
  'Company Nine [1980 - 1989]'
]
*/

const agesSquare = ages.map(age => Math.sqrt(age));
console.log(agesSquare);
/*
[
  5.744562646538029, 3.4641016151377544,
   4.47213595499958,                  4,
   2.23606797749979, 7.3484692283495345,
   4.58257569495584,    6.6332495807108,
  7.810249675906654,  3.605551275463989,
  3.872983346207417,  6.708203932499369,
                  5,                  8,
  5.656854249492381
]
*/
const agesTimesTwo = ages.map(age => age * 2);
console.log(agesTimesTwo);
/*
[ 66,  24,  40, 32, 10, 108, 42, 88, 122, 26, 30, 90, 50, 128, 64]
*/

const ageMap = ages
    .map(age => Math.sqrt(age))
    .map(age => age * 2);
console.log(ageMap);
/*
[
  11.489125293076057,  6.928203230275509,
    8.94427190999916,                  8,
    4.47213595499958, 14.696938456699069,
    9.16515138991168,   13.2664991614216,
  15.620499351813308,  7.211102550927978,
   7.745966692414834, 13.416407864998739,
                  10,                 16,
  11.313708498984761
]
*/

 

 

4. sort

// Sort companies by start year
const sortedCompanies = companies.sort(function(c1, c2){
    if(c1.start > c2.start){
        return 1;
    } else {
        return -1;
    }
});
console.log(sortedCompanies);

/*
[
  { name: 'Company Nine', category: 'Retail', start: 1980, end: 1989 },
  { name: 'Company One', category: 'Finance', start: 1981, end: 2003 },
  { name: 'Company Four', category: 'Retail', start: 1985, end: 2010 },
  { name: 'Company Seven', category: 'Auto', start: 1986, end: 1998 },
  { name: 'Company Two', category: 'Retail', start: 1992, end: 2008 },
  { name: 'Company Three', category: 'Auto', start: 1999, end: 2007 },
  { name: 'Company Six', category: 'Finance', start: 2000, end: 2015 },
  { name: 'Company Five', category: 'Technology', start: 2009, end: 2017},
  { name: 'Company Eight', category: 'Technology', start: 2011, end: 2018}
]
*/

// more clean code
const sortedCompanies2 = companies.sort((a,b) => (a.start > b.start ? 1 : -1));
console.log(sortedCompanies2);


// Sort ages
const sortAges = ages.sort((a, b) => a - b);
console.log(sortAges);
/*
 [ 5, 12, 13, 15, 16, 20, 21, 25, 32, 33, 44, 45, 54, 61, 64 ]
*/

const sortAges2 = ages.sort((a, b) => b - a);
console.log(sortAges2);
/*
[ 64, 61, 54, 45, 44, 33, 32, 25, 21, 20, 16, 15, 13, 12, 5]
*/

 

 

5. reduce

let ageSum = 0;
for(let i = 0; i < ages.length; i++){
    ageSum += ages[i];
}
console.log(ageSum);
// 460

const ageSum2 = ages.reduce(function(total, age) {
    return total + age;
}, 0);
console.log(ageSum2);
// 460

// more clean code
const ageSum3 = ages.reduce((total, age) => total + age, 0);
console.log(ageSum3);


// Get total years for all companies
const totalYears = companies.reduce(function(total, company){
    return total + (company.end - company.start);
}, 0);
console.log(totalYears);
// 122

// more clean code
const totalYears2 = companies.reduce((total, company) => total + (company.end - company.start), 0);
console.log(totalYears2);



// Combine Methods
const combined = ages
    .map(age => age * 2)
    .filter(age => age >= 40)
    .sort((a, b) => a - b)
    .reduce((a, b) => a + b, 0);

console.log(combined);
// 798