ODIn/Website
9
0
Fork 1
Code Pull requests Releases Wiki Activity

Slide updates

Browse source
This commit is contained in:
Oliver Kennedy 2021-02-04 02:34:28 -05:00
parent e557a4b024
commit 55155f0e71
Signed by: okennedy
GPG key ID: 3E5F9B3ABD3FDB60
2 changed files with 134 additions and 22 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
src/teaching/cse-562/2021sp/index.erb
View file

@ -10,6 +10,7 @@ schedule:
topic: "Scala Primer"
materials:
lecture: https://youtu.be/0TndAT2MkPs
slides: slide/2021-02-04-Scala.html
- date: "Feb. 9"
topic: "Relational Algebra + Spark"
- date: "Feb. 11"

155
src/teaching/cse-562/2021sp/slide/2021-02-04-Scala.erb
View file

@ -5,6 +5,16 @@ date: Feb 4, 2021
---
<section>
<section>
<h3>News</h3>
<p>Checkpoint 0 will be posted tonight or tomorrow.</p>
<p>Class actually starts at 12:45 (but I'll be around from 12:30 to answer questions).</p>
</section>
<section>
<br/>
</section>
<section>
<h3>My assumptions</h3>
@ -22,10 +32,10 @@ date: Feb 4, 2021
<dl>
<dt>Package</dt>
<dd>An organizational unit clustering related functionality</dd>
<dt>Class</dt>
<dd>A group of related code that applies to entities of a type (Like Java)</dd>
<dt>Object</dt>
<dd>A 'singleton' class. (Like Java's <b>static</b>)</dd>
<dt>Companion Object</dt>
<dd>A 'singleton' class implementing methods related to a class</dd>
<dt>Case Class</dt>
<dd>A class with bonus features (we'll discuss shortly).</dd>
</dl>
@ -38,14 +48,12 @@ date: Feb 4, 2021
<pre><code class="scala">
package edu.buffalo.myapp
import java.io.File
import scala.io._
object MyApp
{
val message: String = "Hello World"
def main(args: Array[String]): Unit = {
println(message)
var stream: Stream = Stream.fromFile(new File("Hello.txt"))
@ -96,7 +104,7 @@ date: Feb 4, 2021
<pre><code class="scala">
class MyClass(name: String, age: Int) {
</code></pre>
Classes are defined much like java, except constructor fields are given directly in the class definitions. e.g., you would instantiate this class as <tt>new MyClass("Bob", "102")</tt>.
Classes are defined much like java, except constructor fields are given directly in the class definitions. e.g., you would instantiate this class as <tt>new MyClass("Bob", 102)</tt>.
</div>
</section>
@ -108,7 +116,7 @@ date: Feb 4, 2021
with MyOtherTrait {
</code></pre>
Inheritence is defined with the <tt>extends</tt> keyword. Like Java, Scala only allows single inheritance, but you add define interfaces and mixins through the <tt>with</tt> keyword.
Inheritence is defined with the <tt>extends</tt> keyword. Like Java, Scala only allows single inheritance, but you add interfaces and mixins through the <tt>with</tt> keyword.
<div class="fragment">
Objects can also use the <tt>extends</tt> and <tt>with</tt> keywords.
@ -267,9 +275,9 @@ date: Feb 4, 2021
<h3>Tuples</h3>
<pre><code class="scala">
val a = (1, "Cookie", "Alice")
val b = (2, "Cake", "Bolesław")
val all = Seq(a, b)
val a = (1, "Cookie", "Alice")
val b: (Int, String, String) = (2, "Cake", "Bolesław")
val all: Seq[(Int, String, String)] = Seq(a, b)
</code></pre>
<p>Scala also has a "Tuple" type (like Python).</p>
@ -286,12 +294,64 @@ date: Feb 4, 2021
<section>
<ul>
<li><tt>.map { v => ... }</tt>: Get a new collection by transforming every element of the collection using the lambda.</li>
<li><tt>.filter { v => ... }</tt>: Get a new collection by deleting every element of the collection on which the lambda returns false.</li>
<li><tt>.flatten</tt>: Assuming the target is a collection of collections, get a new collection by concatenating all of the nested collections.</li>
<li><tt>.toMap</tt>: Convert any collection of 2-tuples to a Map.</li>
<li><tt>.toSeq</tt>: Convert any collection into a sequence.</li>
<li><tt>.toIndexedSeq</tt>: Convert any collection into an indexed sequence.</li>
<li><tt>.toSet</tt>: Convert any collection into a set.</li>
</ul>
</section>
<section>
<p>So how about those immutable collections...</p>
<p class="fragment">Why does a collection need to be mutable?</p>
</section>
<section>
<h3>Common Patterns... </h3>
<pre><code class="java">
public int add_one(collection: List&lt;Int&gt;) {
ArrayList&lt;Int&gt; result = new ArrayList&lt;Int&gt;();
for(element : collection){
result.append(element + 1)
}
return result
}
</code></pre>
</section>
<section>
<tt>.map { v => ... }</tt>: Get a new collection by transforming every element of the collection using the lambda.
<pre><code class="scala">
collection.map { x => x+1 }
</code></pre>
</section>
<section>
<h3>Common Patterns... </h3>
<pre><code class="java">
public int only_big(collection: List&lt;Int&gt;) {
ArrayList&lt;Int&gt; result = new ArrayList&lt;Int&gt;();
for(element : collection){
if(element > 100){
result.append(element)
}
}
return result
}
</code></pre>
</section>
<section>
<tt>.filter { v => ... }</tt>: Get a new collection by deleting every element of the collection on which the lambda returns false.
<pre><code class="scala">
collection.filter { _ > 100 }
</code></pre>
</section>
<section>
<pre><code class="scala">
all.filter { x => x._2.equals("Cookie") }
@ -301,25 +361,49 @@ date: Feb 4, 2021
</section>
<section>
<ul>
<li><tt>.foldLeft(x) { (accum, v) => ... }</tt>: Start with x. Apply the lambda to (x, firstElement) to get a new x. Repeat for every element of the target and return the final value of x.</li>
</ul>
<h3>Common Patterns... </h3>
<pre><code class="java">
public int flatten(collection: List&lt;List&lt;Int&gt;&gt;) {
ArrayList&lt;Int&gt; result = new ArrayList&lt;Int&gt;();
for(nested : collection){
for(element : nested){
result.append(element)
}
}
return result
}
</code></pre>
</section>
<section>
<tt>.flatten</tt>: Assuming the target is a collection of collections, get a new collection by concatenating all of the nested collections.
<pre><code class="scala">
all.fold(0) { (accum, v) => accum + v._1 }
collection.flatten
</code></pre>
Returns <tt>3</tt> (the sum of the first tuple field)
</section>
<section>
<h3>A Shorthand</h3>
<pre><code class="scala">
all.fold(0) { _ + _._1 }
<h3>Common Patterns... </h3>
<pre><code class="java">
public int sum(collection: List&lt;Int&gt;) {
int accum = 0;
for(element : collection){
accum += element
}
return accum
}
</code></pre>
</section>
Underscores can <i>sometimes</i> be used as shorthands for lambda functions when a variable is only used once.
<section>
<tt>.foldLeft(x) { (accum, v) => ... }</tt>: Start with x. Apply the lambda to (x, firstElement) to get a new x. Repeat for every element of the target and return the accumulator.</li>
<pre><code class="scala">
collection.foldLeft(0) { (accum, element) => accum + element }
</code></pre>
<pre class="fragment"><code class="scala">
collection.foldLeft(0) { _ + _ }
</code></pre>
</section>
</section>
@ -377,7 +461,8 @@ date: Feb 4, 2021
val myFoo = Foo("Abe", 1)
</code></pre>
<p>For example, you don't need to use "new" to construct one.</p>
<p>For example, you don't need to use "new" to construct one</p>
<p>and accessors are defined for all of the constructor variables.</p>
</section>
<section>
@ -451,7 +536,33 @@ organization := "edu.buffalo.cse.odin",
</code></pre>
</section>
<section>
<h3>Testing</h3>
<p><a href="http://etorreborre.github.io/specs2/">Specs2</a> is my unit testing-framework of choice.</p>
<pre><code class="scala">
class HelloWorldSpec extends Specification {
"This is a specification for the 'Hello world' string".txt
"The 'Hello world' string should" >> {
"contain 11 characters" >> {
"Hello world" must haveSize(11)
}
"start with 'Hello'" >> {
"Hello world" must startWith("Hello")
}
"end with 'world'" >> {
"Hello world" must endWith("world")
}
}
}
</code></pre>
</section>
<section>
<p>Many IDEs provide SBT integration. See the Scala <a href="https://docs.scala-lang.org/getting-started/index.html">Getting Started Page</a> and Scala <a href="https://scalameta.org/metals/">Metals Page</a> for more details.</p>
<p>If you prefer a text editor, check out <a href="https://scalacenter.github.io/bloop/">Bloop</a>.</p>
</section>
</section>