panpsychism/unit_01/w02d02/morning_exercise

W02D02 Morning Warmup

JAVASCRIPT ITERATORS

#####.forEach, .map, and .reduce

Javascript iterators are like loops. They step (or iterate) over each item in an array. Iterators perform operations according to conditions specified in a callback.

.forEach

.forEach is the basic iterator, all it does is step through each item in an array.

EXAMPLE:

arr = [8, 8, 8, 8, 8, 8, 8, 8];

arr.forEach(function(n) {
	console.log(n + 1);
});

=> Prints a bunch of 9s to the console

EXERCISE:

• Log each word in words in upper case using .forEach.

words = ["Ho", "Chi", "Minh", "City", "was", "once", "known", "as", "Prey", "Nokor"];

.map

.map is like .forEach but it returns a new array with the selections and / or transformations applied in the iterator. .map saves to a new array and does not alter the original array.

EXAMPLE:

var new_arr = arr.map(function(n) {
	return n += n / 2
});

=> [12, 12, 12, 12, 12, 12, 12, 12]

####EXERCISE:

more_words = ["Joe", "Overreats", "Eggs"];

• Map to a new array that stores only the first letter from each word in more_words.

Expected result:

["J", "O", "E"]

...

.reduce

.reduce iterates over the elements in an array and smooshes them together into a single variable according to the instructions in the iterator. Like .map, it returns a new value and does not alter the original array.

EXAMPLE:

Add together all numbers in an array:

arr = [8, 8, 8, 8, 8, 8, 8, 8];

new_value = arr.reduce(function(sum, n){
	return sum += n
});

=> 64

EXERCISE:

arr = [8, 8, 8, 8, 8, 8, 8, 8];

• Return the product of the numbers in arr.

...

EXERCISE:

Using both .map and .reduce, find the total sheepCount of sheep shorn by sheep shearers at the 1623 Sheep Shearing Feast:

var sheepShearers = [
    {
        name: "Tim",
        age: 20,
        sheepCount: 18
    },
    {
        name: "C3PO",
        age: 200,
        sheepCount: 320
    },
    {
        name: "Cousin It",
        age: Infinity,
        sheepCount: 2900
    }
];

=> 3238

FINISHED EARLY?:

Find a value in a given array

• Write a function searchArray that takes an array and value as parameters and searches the array for the given value. If the value is in the array, return true, otherwise return '-1'.

var nums = [1,2,3,4,5]
searchArray(nums, 3) => true
searchArray(nums, 6) => -1

Here is some starter code:

var searchArray = function(array,value) {

};