array

How to drop the first matching element in a Scala sequence

Summary: This blog post shows one way to drop/filter the first matching element from a Scala sequence (Seq, List, Vector, Array, etc.). I don’t claim that the algorithm is efficient, but it does work.

Background

While creating some Scala test code earlier today I had an immutable list of toppings for a pizza, and I got into a situation where I wanted to remove the first instance of a topping.

A “Minority Report” Monte Carlo simulation in Scala

This article shares the source code for a Monte Carlo simulation that I wrote in Scala. It was inspired by the movie Minority Report, as well as my own experience.

Background

For the purposes of this simulation, imagine that you have three people that are each “right” roughly 80% of the time. For instance, if they take a test with 100 questions, each of the three individuals will get 80 of the questions right, although they may not get the same questions right or wrong. Given these three people, my question to several statisticians was, “If two of the people have the same answer to a given question, what are the odds that they are correct? Furthermore, if all three of them give the same answer to a question, what are the odds that they are right?”

A Scala method to write a list of strings to a file

As a brief note today, here’s a Scala method that writes the strings in a list — more accurately, a Seq[String] — to a file:

def writeFile(filename: String, lines: Seq[String]): Unit = {
    val file = new File(filename)
    val bw = new BufferedWriter(new FileWriter(file))
    for (line <- lines) {
        bw.write(line)
    }
    bw.close()
}
Java: Examples of the Java list/array `subList` method (list subset) alvin June 27, 2019 - 12:26pm

As a little note today, if you ever need to extract a subset of a Java list or array, here are some examples of the Java subList method:

How to convert a Java array into a Stream

If you ever need to convert a Java array into a Stream, there are at least two ways to do it.

1) Converting an array to a Stream

First, to convert the entire array to a Stream, use the Stream.of static method like this:

Scala: Generating a sequence/list of all ASCII printable characters

I ran into a couple of interesting things today when trying to generate random alphanumeric strings in Scala, which can be summarized like this. I won’t get into the “random” stuff I was working on, but here are a couple of examples of how to generate lists of alphanumeric/ASCII characters in Scala:

scala> val chars = ('a' to 'Z').toList
chars: List[Char] = List()

scala> val chars = ('A' to 'z').toList
chars: List[Char] = 
List(A, B, C, D, E, F, G, H, I, J, K, L, 
     M, N, O, P, Q, R, S, T, U, V, W, X, 
     Y, Z, [, \, ], ^, _, `, a, b, c, d, 
     e, f, g, h, i, j, k, l, m, n, o, p, 
     q, r, s, t, u, v, w, x, y, z)

scala> val chars = (' ' to 'z').toList
chars: List[Char] = 
List( , !, ", #, $, %, &, ', (, ), *, +, 
     ,, -, ., /, 0, 1, 2, 3, 4, 5, 6, 7, 
     8, 9, :, ;, <, =, >, ?, @, A, B, C, 
     D, E, F, G, H, I, J, K, L, M, N, O, 
     P, Q, R, S, T, U, V, W, X, Y, Z, [, 
     \, ], ^, _, `, a, b, c, d, e, f, g, 
     h, i, j, k, l, m, n, o, p, q, r, s, 
     t, u, v, w, x, y, z)

Scala: Convert a String with newline characters to a sequence/list of strings

If you ever need a Scala method/function to convert a string with newline characters in it to a sequence of strings (Seq[String]), here you go:

def convertStringWithNewlinesToSeq(s: String): Seq[String] =
    s.split("\n").toVector

You can convert the final result to a Vector, Seq, List, ArrayBuffer, Array, etc., but I prefer Vector. The Scala REPL demonstrates how it works:

scala> convertStringWithNewlinesToSeq("")
res0: Seq[String] = Vector("")

scala> convertStringWithNewlinesToSeq("foo")
res1: Seq[String] = Vector(foo)

scala> convertStringWithNewlinesToSeq("foo\nbar\nbaz")
res2: Seq[String] = Vector(foo, bar, baz)

scala> convertStringWithNewlinesToSeq("foo\nbar\nbaz\n\n")
res3: Seq[String] = Vector(foo, bar, baz)

Kotlin sortedWith syntax and lambda examples

As a quick note, here’s an example of how to use the Kotlin sortedWith syntax with an anonymous function (lambda). Given this list of integers:

val list = listOf(7,3,5,9,1,3)

Here’s an example of how to use sortedWith using a Comparator and lambda:

Kotlin sortedBy syntax and examples

As a quick note, here’s an example of the Kotlin sortedBy syntax. Given this list of strings:

val names = listOf("kim", "julia", "jim", "hala")

the comments after these examples show how the Kotlin sortedBy function works:

Kotlin: Convert a list to a String (joinToString syntax/example)

Here’s a little Kotlin joinToString example. First, a sample list to work with:

val nums = listOf(1,2,3,4,5)

Then here’s the joinToString example:

nums.joinToString(
    separator = ", ",
    prefix = "[",
    postfix = "]",
    limit = 3,
    truncated = "there’s more ..."
)

When you put all of that code in the Kotlin REPL you’ll see this result: