Functional programming warmup

Overview

In this experience, you will explore functional programming concepts through Underscore. Before starting:

Please listen to the Functional Programming for Java and C++ Programmers screencast.
Please go through the readings on Underscore so you have some basic familiarity with the library.

Set up JSFiddle with Underscore

To play around with Underscore, open up JSFiddle, click on the settings button associated with the Javascript window, and select “Underscore 1.8.3” to load Underscore into your JSFiddle. Here’s what it should look like:

To verify that Underscore is available in your JSFiddle, invoke an underscore function (such as identity()) and log the output to the console. For example:

Play around with Underscore

Here are some simple function definitions with a link to which Underscore utility to use. Each are only a few lines of code and should take you less than a minute to write.

1. helloEveryone

Use each to implement a function called helloEveryone that accepts a list of objects and prints out “Hello” followed by the object to the console.

helloEveryone(["joe", "mary"]);
// prints to console:
// Hello joe
// Hello mary

2. addFive

Use map to implement a function called addFive that accepts a list of numbers and returns that list of numbers incremented by five.

addFive([1, 2, 3, 4, 5]);
// [6, 7, 8, 9, 10]

3. concat

Use reduce to implement a function called concat that accepts a list of strings and returns a single string that is the concatenation of that list.

concat(["1", "2", "3"]);
// "123"

4. longString

Use find to implement a function called longString that accepts a list of strings and returns the first string that is longer than 10 characters.

longString(["1", "2", "3000000000000000", "44444444444444444444444"]);
// "3000000000000000"

5. longStrings

Use filter to implement a function called longStrings that accepts a list of strings and returns all the strings that are longer than 10 characters.

longStrings(["1", "2", "3000000000000000", "44444444444444444444444"]);
// ["3000000000000000", "44444444444444444444444"]

6. hasFoo

Use contains to implement a function called hasFoo that accepts a list of strings and returns true if there is at least one occurrence of “Foo” in the list.

hasFoo(["1", "2", "3000000000000000", "44444444444444444444444", "Foo"]);
// true

7. allBig

Use every to implement a function called allBig that accepts a list of objects and returns true if the value of every num field in the list is greater than 100.

allBig([{num: 101}, {num: 1000, name: "Roy"} ]);
// true

8. fishNames

Use pluck and uniq to implement a function called fishNames that accepts a list of objects and returns a list of the values of the fish field with duplicates removed.

fishNames([{fish: "Ahi", num: 100}, {fish: "Ahi", num: 10000}, {fish: "Opah", num: 800}, {fish: "Opah", num: 350} ]);
// ["Ahi", "Opah"]

9. mostFishList

Use sortBy to implement a function called mostFishList that accepts a list of objects and returns a new list in which the objects are ordered by the num field.

mostFishList([{fish: "Ahi", num: 100}, {fish: "Ahi", num: 10000}, {fish: "Opah", num: 800}, {fish: "Opah", num: 350}]);
// [{fish: "Ahi", num: 100}, {fish: "Opah", num: 350}, {fish: "Opah", num: 800}, {fish: "Ahi", num: 10000}]

10. fishGroups

Use groupBy to implement a function called fishGroups that accepts a list of objects and returns an object in which the original objects are now grouped by fish name.

fishGroups([{fish: "Ahi", num: 100}, {fish: "Ahi", num: 10000}, {fish: "Opah", num: 800}, {fish: "Opah", num: 350}]);
// {"Ahi": [{fish: "Ahi", num: 100}, {fish: "Ahi", num: 10000}], "Opah": [{fish: "Opah", num: 800}, {fish: "Opah", num: 350}]]

11. numFish

Use pluck and reduce to implement a function called numFish that accepts a list of objects containing fish data, plucks the values of the num field, then reduces that list of fish numbers to return the total number of fish.

numFish([{fish: "Ahi", num: 100}, {fish: "Ahi", num: 10000}, {fish: "Opah", num: 800}, {fish: "Opah", num: 350}]);
// 11250

Submission instructions

You will not submit anything for this experience. It’s just a warmup to get you comfortable using Underscore function. That doesn’t make this an “optional” assignment: if you skip this one, you will find the other assignments significantly more difficult!