Lists and Arrays and Methods 2 17 2012 Opening Discussion Do you have any questions about the quiz Minute essay comments Other collection types Gandalf vs Dumbledore Approaching problems Difference between recursion and loops Cutting a Double to a number of digits Do you need to improve your recursive methods Not knowing what to ask Infinite arrays or undefined length More TA Kristen Lund Anti virus recommendation Array size limit Filling an array with user input Grading assignments Heterogeneous arrays and lists Default case for match Cyber attack of automated cars Lab hours on weekends Recap Arrays and Lists Creation Array 5 7 4 List 8 5 3 new Array Double 1000 1 2 3 Nil Comparison Arrays mutable fixed size Lists immutable to make new longer list Indexing start at 0 arr 5 arr 5 hi Using Lists You can do direct access on lists but it is inefficient The better method is to use the head and tail methods The elements in a list can t be changed However you can efficiently add new elements at the front to make a new list Lists work very well with recursion List and Array Patterns You can make patterns with Lists and Arrays For Arrays Array 1 2 a b c For Lists List 1 2 a b c h t matches any non empty list Nil matches an empty list Standard Methods There are lots of methods on collections The API can help us see all of them Part of collections Boolean tests contains endsWith isEmpty nonEmpty startsWith Searching drop init last slice splitAt take takeRight indexOf lastIndexOf Other mkString reverse zip zipWithIndex Other Methods If the elements in a list support addition or multiplication you can use the sum and product methods If they are ordered you can do min and max Having sum and length makes averages really easy With min you can even drop a grade easily Higher Order Methods The most powerful methods are ones you can pass functions into exists forall Boolean checks like for math filter partition separate collection based on Boolean map apply function to all the elements reduceLeft apply function moving through collection foldLeft apply function moving through but allows initial value so it can return a different type This is curried Let s Put These Into Action I want to spend the rest of the class time playing with these methods and seeing what we can do with them A String is a collection so you can do these things with a String as well String also has a method called split Minute Essay What questions do you have What collection method made the least sense
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