Higher Order Functions

Hi. 0:00 In the next two videos, we'll learn about higher order functions. 0:01 Higher order functions are functions that take other functions as parameters. 0:05 In the first video, we'll focus on using built In higher order functions. 0:10 Whereas in the second video, we'll create our own. 0:14 You may have noticed in earlier stages that in certain locations, 0:18 I used the foreach function to print elements in a collection. 0:21 Foreach is a high order function which takes another function as a parameter. 0:25 Let's take a look. 0:30 Let's recall our heroes array from an earlier lesson, when we called for 0:32 each on our heroes array, it would bring out every element in the array, 0:37 let's dive back into the code and take a look. 0:41 As we've noticed earlier, 1:04 we call the foreach function on the heros array then we pass in 1:06 the print line function and this in total prints out every element in our array. 1:09 Let's recompile our app and check out the results. 1:15 There are many other useful higher order functions in Scala, let's dive into them. 1:19 One of the ones I find myself using most is map. 1:25 Map allows us to apply a function to each element in a collection. 1:29 For example, if we have an array of elements, and we call them .mapfunction, 1:34 we iterate through the array and can perform actions on each element. 1:39 For instance, we created a function to convert each element in the array 1:44 to lowercase in order to achieve our result 1:48 we had to loop throughout the collection using a four loop. 1:52 However, now we can achieve the same result in a much more concise approach 1:55 using map. 1:59 Let's take a look. 2:00 In this line, we take the heroes array and call the map function on it to iterate 2:14 throughout all the elements of the collection and for 2:18 each one of these elements, we convert them to lower case. 2:21 Another way to write the above function literal is to use an underscore. 2:25 Think of an underscore as a wildcard which refers to the elements being iterated on. 2:30 Let's take a look at that. 2:35 Let's re-run our app and check out the results. 3:00 As expected, every element in the array, is lowercase, however, 3:06 this code is in a way more concise than what we had previously. 3:10 Another useful higher order function is filter. 3:14 Filter takes a function that returns a Boolean and builds a new collection in for 3:17 which the predicate is true. 3:22 In this case, we filter for 3:38 all the superheros that contain the string man in their name. 3:40 Let's take a look at the result. 3:44 Awesome. 3:51 As expected we got all the elements except for Thor. 3:52 Learning about higher order functions is great but 3:56 they become way more powerful if 4:04 we can learn how to use them together. 4:09 In this instance, we use the filter to grab only sent elements we want. 4:25 And then map to iterate to reach one nd return their value in upper case. 4:30 To dive in a little bit more detail, filter takes a function called contains 4:34 which checks if the string man exists, and then map takes a function 4:40 called two uppercase to convert the characters of the elements to uppercase. 4:45 Let's recompile our app and check out the results. 4:50 Awesome, as expected we filtered every element and 4:59 made sure that we only got back the ones containing the key word man. 5:02 And we're also able to change them to all upper case. 5:07 There are many other useful higher order functions such as count, drop while, drop 5:11 Index where which we can get familiar with by implementing an array of integeres. 5:16 Let's create an array of integers to get familiar with some of the higher order 5:22 functions we just mentioned. 5:26 Great, the first one we'll use is dropWhile, which loops 5:39 through the collection and drops any elements that do not satisfy a predicate. 5:43 In this case, any element less than three. 5:48 As expected, we drop any elements that were less than the value three, 6:07 hence number one and two are no longer in our array. 6:12 Another function, count, counts the number of elements that match the predicate. 6:16 In our case we'll check how many elements are less than or equal to four. 6:20 Let's recompile our app and check out our results. 6:36 Awesome. 6:46 As we can see, the numbers.count function returned seven elements and that's 6:47 because there's seven elements in the array that are less than or equal to four. 6:51 Another useful function is index ware. 6:56 Index ware returns the index of the element found or 6:59 a negative one if the element is not in the collection. 7:02 Let's take a look. 7:05 Awesome. 7:30 As expected, the value three is found in index two. 7:31 Remember, arrays are zero based even in scalar. 7:35 Great, we learned about higher order functions in Scala. 7:39 In the next video we'll create our own higher order function and 7:42 use it in our code. 7:46 See you here. 7:47