Interview Prep - Iterators

Today you'll be implementing even more iterator functions on the whiteboard in groups of three. Since there are three problems, each group member should take a turn "driving" for one problem with the other two as support ("navigators").

Note: DO NOT use any built-in iterator functions from Underscore or another library. You will often be asked in interviews to implement well-known methods like this from scratch as problem-solving exercises.

How to Get Started

• Use pseudo-code to plan the logic of your function before writing actual code on the board.

• Write down at least one new example of test input, and write down the expected output. Hint: For filter and partition, one of your test inputs will be a function.

• Only when you have pseudo-code and test input with expected output should you write code to implement the body of the function.

Problems

1. filter(arr, truthTest)

   
    function isEven(num){
        return num % 2 === 0;
    }
   
    filter([1, 2, 3, 4, 5, 6], isEven);
   
    // => [2, 4, 6]
   

   Write a function called filter that takes in an array and another function (a truth test). filter should iterate through the array, check whether each value passes the truth test function, and return a new array containing all the values that passed.

1. partition(arr, truthTest)

```js
function isOdd(num){
    return num % 2 !== 0;
}

partition([0, 1, 2, 3, 4, 5], isOdd);
// => [[1, 3, 5], [0, 2, 4]]
```

Write a function called `partition` that takes in an array and another function (a truth test).  `partition` should split the array into two groups: one whose elements all pass the truth test and one whose elements all fail. It should return a new array with the two groups nested inside.

1. pluck(arr, key)

    grandparents = [
        {first: "June", last: "Crane", age: 74},
        {first: "Jim", last: "Crane", age:76},
        {first: "Linda", "Fuentes", age: 62},
        {first: "Panfilo", "Fuentes", age: 76}
        ];
   
    pluck(grandparents, 'first');
    // =>["June", "Jim", "Linda", "Panfilo"]
   

   Write a function called pluck that takes in an array of objects and a key. pluck should iterate through the array, pick out the value each object has associated with the given key, and return a new array containing those values.

   1. Optional Stretch: where(arr, properties)

      ```js

   events = [

    {location: "Yerba Buena", day: "Wednesday", time: "0900"},
    {location: "GA", day: "Tuesday", time: "1830"},
    {location: "Blue Bottle", day: "Tuesday", time: "1100"},
    {location: "GA", day: "Thursday", time: "1830"},
    {location: "GA", day "Thursday", time: "0917"}
    ];
   

   where(events, {time: "1830", location: "GA"}); // => [ // {location: "GA", day: "Tuesday", time: "1830"}, // {location: "GA", day: "Thursday", time: "1830"} // ] ```

Write a function called `where` that takes an array of objects and another object. `where` looks through each object in the array, returning a new array containing the objects that match *every* key-value pair given in the second argument.

Hint: Remember looping through objects with "for in" loops and "hasOwnProperty"? If not, you'll need to look it up!