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148 lines
2.6 KiB
148 lines
2.6 KiB
# W02D02 Morning Warmup
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# JAVASCRIPT ITERATORS
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#####`.forEach`, `.map`, and `.reduce`
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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.
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# .forEach
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`.forEach` is the basic iterator, all it does is step through each item in an array.
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#### EXAMPLE:
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```
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arr = [8, 8, 8, 8, 8, 8, 8, 8];
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arr.forEach(function(n) {
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console.log(n + 1);
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});
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=> Prints a bunch of 9s to the console
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```
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##### EXERCISE:
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- Log each word in `words` in upper case using `.forEach.`
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```
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words = ["Ho", "Chi", "Minh", "City", "was", "once", "known", "as", "Prey", "Nokor"];
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```
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# .map
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`.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.
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EXAMPLE:
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```
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var new_arr = arr.map(function(n) {
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return n += n / 2
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});
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=> [12, 12, 12, 12, 12, 12, 12, 12]
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```
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####EXERCISE:
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```
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more_words = ["Joe", "Overreats", "Eggs"];
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```
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- Map to a new array that stores only the first letter from each word in `more_words`.
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Expected result:
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```
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["J", "O", "E"]
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```
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...
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# .reduce
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`.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.
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#### EXAMPLE:
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Add together all numbers in an array:
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```
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arr = [8, 8, 8, 8, 8, 8, 8, 8];
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new_value = arr.reduce(function(sum, n){
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return sum += n
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});
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=> 64
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```
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#### EXERCISE:
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```
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arr = [8, 8, 8, 8, 8, 8, 8, 8];
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```
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- Return the *product* of the numbers in `arr`.
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...
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#### EXERCISE:
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Using both `.map` and `.reduce`, find the total sheepCount of sheep shorn by sheep shearers at the 1623 Sheep Shearing Feast:
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```
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var sheepShearers = [
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{
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name: "Tim",
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age: 20,
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sheepCount: 18
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},
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{
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name: "C3PO",
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age: 200,
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sheepCount: 320
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},
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{
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name: "Cousin It",
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age: Infinity,
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sheepCount: 2900
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}
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];
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```
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```
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=> 3238
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```
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#### FINISHED EARLY?:
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Find a value in a given array
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- 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'.
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```javascript
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var nums = [1,2,3,4,5]
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searchArray(nums, 3) => true
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searchArray(nums, 6) => -1
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```
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Here is some starter code:
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```javascript
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var searchArray = function(array,value) {
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};
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```
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