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fp:lab04 [2022/03/09 20:26] pdmatei |
fp:lab04 [2022/05/15 23:54] (current) vbadoiu old revision restored (2022/03/25 10:15) |
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| ===== 4. Lists in Scala ===== | ===== 4. Lists in Scala ===== | ||
| + | |||
| + | Objectives: | ||
| + | * get familiar with **pattern matching** lists, as well as common list operations from Scala and how they work | ||
| + | * get familiar with common **higher-order functions** over lists (partition, map, foldRight, foldLeft, filter) | ||
| ==== 4.1. Common list operations ==== | ==== 4.1. Common list operations ==== | ||
| - | **4.1.1.* Write a function which returns true if a list of integers has at least k elements. Use patterns. | + | **4.1.1.** Write a function which returns true if a list of integers has at least k elements. Use patterns. |
| <code scala> | <code scala> | ||
| def atLeastk(k: Int, l: List[Int]): Boolean = | def atLeastk(k: Int, l: List[Int]): Boolean = | ||
| Line 14: | Line 18: | ||
| <code scala> | <code scala> | ||
| def take(n: Int, l: List[Int]): List[Int] = ??? | def take(n: Int, l: List[Int]): List[Int] = ??? | ||
| - | //take(3,List(1,2,3,4,5)) = 3 | + | //take(3,List(1,2,3,4,5)) = List(1,2,3) |
| </code> | </code> | ||
| Line 35: | Line 39: | ||
| </code> | </code> | ||
| + | ==== 4.2. Gradebooks ==== | ||
| + | More general implementation of ''taken'', ''dropn'' and ''part'' are already implemented in Scala and can be used as member functions of lists. Examples are shown below: | ||
| + | <code scala> | ||
| + | val l = List(1,2,3,4,5,6,7,8,9) | ||
| + | l.take(3) | ||
| + | l.drop(3) | ||
| + | l.partition(_%2 == 0) | ||
| + | </code> | ||
| + | In what follows, we shall encode a gradebook as a list of pairs ''(<name>,<grade>)'', where ''<name>'' is a String and ''<grade>'' is an Int. Example: | ||
| + | <code scala> | ||
| + | val gradebook = List(("G",3), ("F", 10), ("M",6), ("P",4)) | ||
| + | </code> | ||
| + | |||
| + | To make the type signatures more legible, we can introduce type aliases in Scala: | ||
| + | <code scala> | ||
| + | type Gradebook = List[(String,Int)] //the type Gradebook now refers to a list of pairs of String and Int | ||
| + | </code> | ||
| + | Add this type alias to your code before solving the following exercises. | ||
| + | |||
| + | **4.2.1.** Write a function which adds one point to all students which have a passing grade (>= 5), and leaves all other grades unchanged. | ||
| + | <code scala> | ||
| + | def increment(g: Gradebook): Gradebook = | ||
| + | g.map(???) | ||
| + | </code> | ||
| + | |||
| + | **4.2.2.** Find the average grade from a gradebook. You must use ''foldRight''. | ||
| + | <code scala> | ||
| + | def average(g: Gradebook): Double = ??? | ||
| + | </code> | ||
| + | |||
| + | **4.2.3.** Write a function which takes a gradebook and returns the percentage of failed vs. passed students, as a pair (x,y). | ||
| + | <code scala> | ||
| + | def percentage(g: Gradebook): (Double,Double) = ??? | ||
| + | </code> | ||
| + | |||
| + | **4.2.4.** Write a function which takes a gradebook and returns the list of names which have passed. Use filter and map from Scala. | ||
| + | <code scala> | ||
| + | def pass(g: Gradebook): List[String] = ??? | ||
| + | </code> | ||
| + | |||
| + | **4.2.5.** Implement merge-sort (in ascending order) over gradebooks: | ||
| + | <code scala> | ||
| + | def mergeSort(l: Gradebook): Gradebook = { | ||
| + | def merge(u: Gradebook, v: Gradebook): Gradebook = ??? | ||
| + | ??? | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | **4.2.6** Write a function which takes a gradebook and reports all passing students in **descending** order of their grade. | ||
| + | <code scala> | ||
| + | def honorsList(g: Gradebook): List[String] = ??? | ||
| + | </code> | ||