populate

How to create and populate Kotlin lists (initialize mutable and immutable lists)

If you ever need to create and populate a Kotlin list, I can confirm that these approaches work for an immutable and mutable lists:

// fill an immutable list
val doubles = List(5) { i -> i * 2 }

// fill a mutable list of ten elements with zeros
val ints = MutableList(10) { 0 }

The Kotlin REPL shows how these approaches work:

Scala List class: methods, examples, and syntax

This page contains a large collection of examples of how to use the methods on the Scala List class.

The Scala List class as an immutable, linear, linked-list class. It’s very efficient when it makes sense for your algorithms to (a) prepend all new elements, (b) work with it in terms of its head and tail elements, and (c) use functional methods that traverse the list from beginning to end, such as filter, map, foldLeft, reduceLeft.

Scala Seq class: methods, examples, and syntax

This page contains a large collection of examples of how to use the methods on the Scala Seq class.

Important note about Seq, IndexedSeq, and LinearSeq

As an important note, I use Seq in the following examples to keep things simple, but in your code you should be more precise and use IndexedSeq or LinearSeq where appropriate. As the Seq class Scaladoc states:

How to populate a Scala List with sample data (examples)

As a quick note, I was just reminded that you can populate a Scala List using a Range, like this:

scala> (1 to 5).toList
res0: List[Int] = List(1, 2, 3, 4, 5)

scala> (1 to 10 by 2).toList
res1: List[Int] = List(1, 3, 5, 7, 9)

scala> (5 to 11).toList
res2: List[Int] = List(5, 6, 7, 8, 9, 10, 11)

scala> ('d' to 'h').toList
res3: List[Char] = List(d, e, f, g, h)

Those are just a few examples. For many more ways to populate Scala lists with sample data, see How to populate Scala collections with a Range, How to generate random numbers, characters, and sequences in Scala, and Different ways to create and populate Lists in Scala.

Scala: How to fill/populate a list (same element or different elements)

As a quick note, if you ever need to fill/populate a Scala list with the same element X number of times, one solution is to use the fill method that’s available to Scala sequences, like this:

scala> val x = List.fill(3)("foo")
x: List[String] = List(foo, foo, foo)

If you want to populate a list with different element values, another approach is to use the tabulate method:

A simple way to populate an Android ListView with a SQLite database Cursor

Here’s an example of how to populate an Android ListView, where I get the data for the ListView from a database Cursor:

DatabaseHelper.TeamsCursor tc = DatabaseManager.get(getActivity()).getAllTeams();
ArrayList<String> listOfTeamNames = new ArrayList<>();
for(tc.moveToFirst(); !tc.isAfterLast(); tc.moveToNext()) {
    listOfTeamNames.add(tc.getTeam().teamName);
}

// list the team names with an adapter that talks to our listview
TeamNamesAdapter adapter = new TeamNamesAdapter(listOfTeamNames);
setListAdapter(adapter);

There are more formal ways to create an adapter class to work with a Cursor, but for my needs I just needed to get a list of names from a SQLite database table and show them in a simple ListView — part of a ListFragment — and this was the simplest code to write.

FWIW, the example also shows one way to iterate over the elements in a Cursor using a Java for loop.