FoldLeft is like reduceLeft, but it takes an additional argument and accumulator named z here. The function reduceLeft is defined in terms of our more general function foldLeft. So sum would be zero followed by excess reduceLeft with plus and product would be 1 followed by xs reduceLeft and multiply. So with that, sum and product can also be expressed like this, which is aesthetically a bit more pleasing. Once you hit a pair of parenthesis, you insert a parameter section, one parameter for each underscore that you have encountered. You know the occurrences of an underscore. So this thing here would be inserted at the next outer pair of parentheses or the whole expression if there are no enclosing parenthesis. Every underscoring the formula represents a new parameter going from left to right and the parameters are then defined. Instead of xy arrow x times y for instance, one can also write shorter underscored times underscore. As an aside, we can write these functions that we pass to other functions also in a shorter way. And product would be 1 and xs reduceLeft with the multiplication function. Sum would be just 0 cons xs reduceLeft with the summation function. If you have reduceLeft then we can simplify sum of the product as you see here. And that would give you x1.op, x2.op, x3 and so on until op(xn). So if you have a list of x1 to xn and you do a reduceLeft with op. ReduceLeft inserts a given binary operator between radiation elements of a list. This pattern can be abstracted out using the generic method to reduce left. Otherwise, if it's a list starting with y, it's y plus sum of the remaining elements ys. Sum xs takes a list of inputs towards an end. So for instance, for sum it would look like this. We can implement this with the usual recursive schema. Or to take the products of all elements you would arrive at this formula, multiply all the elements of the list and multiply by 1, which gives you 1 for the empty list. And for the empty list it would return zero. For instance, to sum all the elements of a list, he could use an operation like this one, so x1 plus xn. In fact, it's quite common to combine the elements of a list with a given operator. In this session, we're going to look at another set of operators that serve for reducing lists. ![]() ![]() Last, you should have some familiarity with using the command line. ![]() You should have some background in mathematics (e.g., algebra, logic, proof by induction). ![]() Proficiency with Java or C# is ideal, but experience with other languages such as C/C++, Python, Javascript, or Ruby is also sufficient. Recommended background: You should have at least one year of programming experience. The course is complemented by a series of programming projects as homework assignments. The course is hands-on most units introduce short programs that serve as illustrations of important concepts and invite you to play with them, modifying and improving them. You will also develop a solid foundation for reasoning about functional programs, by touching upon proofs of invariants and the tracing of execution symbolically. In this course, you will discover the elements of the functional programming style and learn how to apply them usefully in your daily programming tasks, such as modeling business domains or implementing business logic. It provides the core infrastructure for sites such as Twitter, Netflix, Zalando, and also Coursera. Scala is the implementation language of many important frameworks, including Apache Spark, Kafka, and Akka. It interoperates seamlessly with both Java and Javascript. Scala fuses functional and object-oriented programming in a practical package. This trend is driven by the adoption of Scala as the main programming language for many applications. Functional programming is becoming increasingly widespread in industry.
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