Spark Scala Cheat Sheet

30-04-2021 admin

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Scala Cheatsheet Thanks to Brendan O’Connor, this cheatsheet aims to be a quick reference of Scala syntactic constructions. Licensed by Brendan O’Connor under a CC-BY-SA 3.0 license. GET OUR BOOKS: - BUY Scala For Beginners This book provides a step-by-step guide for the complete beginner to learn Scala. It is particularly useful to programmers, data scientists, big data engineers, students, or just about anyone who wants to get up to speed fast with Scala (especially within an enterprise context).

Timecomputers driver download for windows. Thanks to Brendan O’Connor, this cheatsheet aims to be a quick reference of Scala syntactic constructions. Licensed by Brendan O’Connor under a CC-BY-SA 3.0 license.

variables
Good	Variable.
Bad	Constant.
Explicit type.
functions
Good Bad	Define function. Hidden error: without `=` it’s a procedure returning `Unit`; causes havoc. Deprecated in Scala 2.13.
Good Bad	Define function. Syntax error: need types for every arg.
Type alias.
vs.	Call-by-value. Call-by-name (lazy parameters).
Anonymous function.
vs.	Anonymous function: underscore is positionally matched arg.
Anonymous function: to use an arg twice, have to name it.
Anonymous function: block style returns last expression.
Anonymous functions: pipeline style (or parens too).
	Anonymous functions: to pass in multiple blocks, need outer parens.
Currying, obvious syntax.
Currying, obvious syntax.
Currying, sugar syntax. But then:
Need trailing underscore to get the partial, only for the sugar version.
Generic type.
	Infix sugar.
Varargs.
packages
Wildcard import.
	Selective import.
Renaming import.
Import all from `java.util` except `Date`.
At start of file: Packaging by scope: Package singleton:	Declare a package.
data structures
Tuple literal (`Tuple3`).
Destructuring bind: tuple unpacking via pattern matching.
Bad	Hidden error: each assigned to the entire tuple.
List (immutable).
Paren indexing (slides).
Cons.
same as	Range sugar.
Empty parens is singleton value of the Unit type. Equivalent to `void` in C and Java.
control constructs
Conditional.
same as	Conditional sugar.
While loop.
Do-while loop.
Break (slides).
same as	For-comprehension: filter/map.
same as	For-comprehension: destructuring bind.
same as	For-comprehension: cross product.
For-comprehension: imperative-ish. `sprintf` style.
For-comprehension: iterate including the upper bound.
For-comprehension: iterate omitting the upper bound.
pattern matching
Good Bad	Use case in function args for pattern matching.
Bad	`v42` is interpreted as a name matching any Int value, and “42” is printed.
Good	`v42` with backticks is interpreted as the existing val `v42`, and “Not 42” is printed.
Good	`UppercaseVal` is treated as an existing val, rather than a new pattern variable, because it starts with an uppercase letter. Thus, the value contained within `UppercaseVal` is checked against `3`, and “Not 42” is printed.
object orientation
Constructor params - `x` is only available in class body.
	Constructor params - automatic public member defined.
Constructor is class body. Declare a public member. Declare a gettable but not settable member. Declare a private member. Alternative constructor.
Anonymous class.
Define an abstract class (non-createable).
Define an inherited class.
	Inheritance and constructor params (wishlist: automatically pass-up params by default).
Define a singleton (module-like).
	Traits. Interfaces-with-implementation. No constructor params. mixin-able.
	Multiple traits.
Must declare method overrides.
Create object.
Bad Good	Type error: abstract type. Instead, convention: callable factory shadowing the type.
Class literal.
Type check (runtime).
Type cast (runtime).
Ascription (compile time).
options
Construct a non empty optional value.
The singleton empty optional value.
but	Null-safe optional value factory.
same as	Explicit type for empty optional value. Factory for empty optional value.
Pipeline style.
For-comprehension syntax.
same as	Apply a function on the optional value.
same as	Same as map but function must return an optional value.
same as	Extract nested option.
same as	Apply a procedure on optional value.
same as	Apply function on optional value, return default if empty.
same as	Apply partial pattern match on optional value.
same as	`true` if not empty.
same as	`true` if empty.
same as	`true` if not empty.
same as	`0` if empty, otherwise `1`.
same as	Evaluate and return alternate optional value if empty.
same as	Evaluate and return default value if empty.
same as	Return value, throw exception if empty.
same as	Return value, `null` if empty.
same as	Optional value satisfies predicate.
same as	Optional value doesn't satisfy predicate.
same as	Apply predicate on optional value or `false` if empty.
same as	Apply predicate on optional value or `true` if empty.
same as	Checks if value equals optional value or `false` if empty.

This post is part of my preparation series for the Cloudera CCA175 exam, “Certified Spark and Hadoop Developer”. Srt marine driver download for windows 10. It is intentionally concise, to serve me as a cheat sheet.

Watchdata driver download for windows. You need familiarity with Python as well as Scala for the Cloudera exam. I have never coded in Scala before, so I am taking this course and preparing a brief Scala summary in this post.

Fortunately, the spark-shell is very helpful in the exam, and you don’t need to compile any .jar files.

Scala Basics

Strings

Regular expressions

Boolean logic

Flow control

Functions