foreach-map-filter.js

/*
Write a function called doubleValues which accepts an array and returns a new array with all the values 
in the array passed to the function doubled

Examples:
    doubleValues([1,2,3]) // [2,4,6]
    doubleValues([5,1,2,3,10]) // [10,2,4,6,20]

*/
function doubleValues(arr){
    const result = [];

    arr.forEach(
        function(val){
            result.push(val * 2);   
        }
    )

    return result;
}

/*
Write a function called onlyEvenValues which accepts an array and returns a new array with only the even 
values in the array passed to the function

Examples:
    onlyEvenValues([1,2,3]) // [2]
    onlyEvenValues([5,1,2,3,10]) // [2,10]

*/
function onlyEvenValues(arr){
    const result = arr.filter(
        function(val){
            return (val % 2 === 0)
        }
    );
    return result;
}

/*
Write a function called showFirstAndLast which accepts an array of strings and returns a new array with 
only the first and last character of each string.

Examples:
    showFirstAndLast(['colt','matt', 'tim', 'test']) // ["ct", "mt", "tm", "tt"]
    showFirstAndLast(['hi', 'goodbye', 'smile']) // ['hi', 'ge', 'se']

*/
function showFirstAndLast(arr){
    const result = arr.map(
        function(val){
            return val[0] + val[val.length - 1]
        }
    );
    return result;
}

/*
Write a function called addKeyAndValue which accepts an array of objects, a key, and a value and returns 
the array passed to the function with the new key and value added for each object 

Examples:
    addKeyAndValue([{name: 'Elie'}, {name: 'Tim'}, {name: 'Matt'}, {name: 'Colt'}], 'title', 'instructor') 
    
    // [{name: 'Elie', title:'instructor'}, {name: 'Tim', title:'instructor'}, {name: 'Matt', title:'instructor'}, {name: 'Colt', title:'instructor'}]

*/
function addKeyAndValue(arr,key,value){
    const result = arr.map(
        function(obj){
            obj[key] = value;
            return obj;
        }
    );
    return result;
}

/*
Write a function called vowelCount which accepts a string and returns an object with the keys as the vowel
and the values as the number of times the vowel appears in the string. This function should be case insensitive
so a lowercase letter and uppercase letter should count.

Examples:
    vowelCount('Elie') // {e:2,i:1};
    vowelCount('Tim') // {i:1};
    vowelCount('Matt') // {a:1})
    vowelCount('hmmm') // {};
    vowelCount('I Am awesome and so are you') // {i: 1, a: 4, e: 3, o: 3, u: 1};
*/
function vowelCount(str){
    const vowelsOnly = [...str].filter(
        function(char){
            return ('aeiou'.indexOf(char.toLowerCase()) !== -1)
        }
    )
    const result = {};
    if (vowelsOnly.length === 0) return result;

    vowelsOnly.forEach(
        function(letter){
            const caseInsen = letter.toLowerCase();
            if (result[caseInsen]){
                result[caseInsen] += 1;
            } else {
                result[caseInsen] = 1;
            }
        }
    );

    return result;
}

/*
Write a function called doubleValuesWithMap which accepts an array and returns a new array with
all the values in the array passed to the function doubled

Examples:
    doubleValuesWithMap([1,2,3]) // [2,4,6]
    doubleValuesWithMap([1,-2,-3]) // [2,-4,-6]
*/

function doubleValuesWithMap(arr) {
    const result = arr.map(
        function(val){
            return val * 2;
        }
    );
    return result;
}

/*
Write a function called valTimesIndex which accepts an array and returns a new array with each
value multiplied by the index it is currently at in the array.

Examples:
    valTimesIndex([1,2,3]) // [0,2,6]
    valTimesIndex([1,-2,-3]) // [0,-2,-6]
*/

function valTimesIndex(arr){
    const result = arr.map(
        function(val, i){
            return(val * i);
        }
    );
    return result;
}

/*
Write a function called extractKey which accepts an array of objects and some key and return
a new array with the value of that key in each object.

Examples:
    extractKey([{name: 'Elie'}, {name: 'Tim'}, {name: 'Matt'}, {name: 'Colt'}], 'name') // ['Elie', 'Tim', 'Matt', 'Colt']
*/

function extractKey(arr, key){
    const result = arr.map(
        function(obj){
            return obj[key];
        }
    );
    return result;
}

/*
Write a function called extractFullName which accepts an array of objects andreturns a new array
with the value of the key with a name of "first" and the value of a key with the name of  "last"
in each object, concatenated together with a space. 

Examples:
    extractFullName([{first: 'Elie', last:"Schoppik"}, {first: 'Tim', last:"Garcia"}, {first: 'Matt', last:"Lane"}, {first: 'Colt', last:"Steele"}]) // ['Elie Schoppik', 'Tim Garcia', 'Matt Lane', 'Colt Steele']
*/

function extractFullName(arr){
    const result = arr.map(
        function(obj){
            return `${obj.first} ${obj.last}`
        }
    );
    return result;
}

/*
Write a function called filterByValue which accepts an array of objects and a key and returns a new
array with all the objects that contain that key.

Examples:
    filterByValue([{first: 'Elie', last:"Schoppik"}, {first: 'Tim', last:"Garcia", isCatOwner: true}, {first: 'Matt', last:"Lane"}, {first: 'Colt', last:"Steele", isCatOwner: true}], 'isCatOwner') // [{first: 'Tim', last:"Garcia", isCatOwner: true}, {first: 'Colt', last:"Steele", isCatOwner: true}]
*/

function filterByValue(arr, key) {
    const result = arr.filter(
        function(obj){
            return (obj[key] !== undefined)
        }
    );
    return result;
}

/*
Write a function called find which accepts an array and a value and returns the first element
in the array that has the same value as the second parameter or undefined if the value is not found in the array.

Examples:
    find([1,2,3,4,5], 3) // 3
    find([1,2,3,4,5], 10) // undefined
*/

function find(arr, searchValue) {
    const result = arr.filter(
        function(val){
            return (val === searchValue);
        }
    );
    if (result.length === 0){
        return undefined;
    } else {
        return result[0];
    }
}

/*
Write a function called findInObj which accepts an array of objects, a key, and some value to search for
and returns the first found value in the array.

Examples:
    findInObj([{first: 'Elie', last:"Schoppik"}, {first: 'Tim', last:"Garcia", isCatOwner: true}, {first: 'Matt', last:"Lane"}, {first: 'Colt', last:"Steele", isCatOwner: true}], 'isCatOwner',true) // {first: 'Tim', last:"Garcia", isCatOwner: true}
*/

function findInObj(arr, key, searchValue) {
    const result = arr.filter(
        function(obj){
            return obj[key] === searchValue;
        }
    )
    return result[0];
}

/*
Write a function called removeVowels which accepts a string and returns a new string with all of the vowels
(both uppercased and lowercased) removed. Every character in the new string should be lowercased.

Examples:
    removeVowels('Elie') // ('l')
    removeVowels('TIM') // ('tm')
    removeVowels('ZZZZZZ') // ('zzzzzz')
*/

function removeVowels(str) {
    let noVowels = [...str].filter(
        function(char){
            return ('aeiou'.indexOf(char.toLowerCase()) === -1);
        }
    ).map(
        function(char){
            return char.toLowerCase();
        }
    )
    return noVowels.join('');
}

/*
Write a function called doubleOddNumbers which accepts an array and returns a new array with all
of the odd numbers doubled (HINT - you can use map and filter to double and then filter the odd numbers).

Examples:
    doubleOddNumbers([1,2,3,4,5]) // [2,6,10]
    doubleOddNumbers([4,4,4,4,4]) // []
*/

function doubleOddNumbers(arr) {
    const odds = arr.filter(
        function(num){
            return (num % 2 !== 0);
        }
    ).map(
        function(num){
            return num * 2;
        }
    );
    return odds;
}