reduce.js

/*
Write a function called extractValue which accepts an array of objects and a key and returns a 
new array with the value of each object at the key.

Examples:
    const arr = [{name: 'Elie'}, {name: 'Tim'}, {name: 'Matt'}, {name: 'Colt'}]
    extractValue(arr,'name') // ['Elie', 'Tim', 'Matt', 'Colt']
*/

function extractValue(arr, key) {

    // map immediately comes to mind :D

    const outValues = arr.reduce(function (fxinArrValues, fxinNextValue) {
        return fxinArrValues.concat(fxinNextValue[key]);
    }, []);

    return outValues;

}


/*
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 outVowelCountObj = str.split('').reduce(function (fxInVowelCounts, nextChar) {
        if ("aeiou".indexOf(nextChar.toLowerCase()) > -1) {
            if (fxInVowelCounts[nextChar]) {
                fxInVowelCounts[nextChar] += 1;
            } else {
                fxInVowelCounts[nextChar] = 1;
            }
        }
        return fxInVowelCounts;
    }, {})

    return outVowelCountObj;

}


/*
Write a function called addKeyAndValue which accepts an array of objects and returns the 
array of objects passed to it with each object now including the key and value passed to the 
function.

Examples:
    const arr = [{name: 'Elie'}, {name: 'Tim'}, {name: 'Matt'}, {name: 'Colt'}];
    
    addKeyAndValue(arr, 'title', 'Instructor') // 
      [
        {title: 'Instructor', name: 'Elie'}, 
        {title: 'Instructor', name: 'Tim'}, 
        {title: 'Instructor', name: 'Matt'}, 
        {title: 'Instructor', name: 'Colt'}
       ]
*/


function addKeyAndValue(arr, key, value) {

    arr = arr.reduce(function (fxinObject, fxinNext) {

        const newObj = fxinNext;
        newObj[key] = value;
        return fxinObject.concat(newObj);

    }, []);

    return arr;

}


/*
Write a function called partition which accepts an array and a callback and returns an array 
with two arrays inside of it. The partition function should run the callback function on 
each value in the array and if the result of the callback function at that specific value is 
true, the value should be placed in the first subarray. If the result of the callback function 
at that specific value is false, the value should be placed in the second subarray. 

Examples:
    
    function isEven(val){
        return val % 2 === 0;
    }
    
    const arr = [1,2,3,4,5,6,7,8];
    
    partition(arr, isEven) // [[2,4,6,8], [1,3,5,7]];
    
    function isLongerThanThreeCharacters(val){
        return val.length > 3;
    }
    
    const names = ['Elie', 'Colt', 'Tim', 'Matt'];
    
    partition(names, isLongerThanThreeCharacters) // [['Elie', 'Colt', 'Matt'], ['Tim']]
*/

function partition(arr, callback) {

    const outPartitionedArray = arr.reduce(function (fxinArrs, fxinVal) {

        if (callback(fxinVal)) {
            return [fxinArrs[0].concat(fxinVal), fxinArrs[1]];
        } else {
            return [fxinArrs[0], fxinArrs[1].concat(fxinVal)];
            //return fxinArrs[1].concat(fxinVal);
        }

    }, [[], []]);

    return outPartitionedArray;

}