tail

Java: A Java list `tail` function (for ArrayList, LinkedList, etc.)

As a brief note today, I was working on a Java/Android application recently, and I needed a “tail” function when I was working on a Java list. What I mean by that is that Scala has a tail function that returns all elements of the list except for the head element, like this:

scala> val x = List(1,2,3,4)
x: List[Int] = List(1, 2, 3, 4)

scala> x.tail
res1: List[Int] = List(2, 3, 4)  //head element removed

and I wanted the same thing in Java.

Scala Vector filtering methods (examples)

This page contains a collection of examples of filtering methods that can be used with a Scala Vector class. I’ll first show a table that describes the filtering methods, and then show examples of them.

How to show the largest files under a directory on Mac OS X (Unix)

Here’s an example that shows how to find the largest files under a directory on MacOS and Linux/Unix systems.

A du/sort command to show the largest files under a directory on Mac OS X

The Unix/Linux command that worked for me on my MacOS system is this:

$ du -a * | sort -r -n | head -10

du is the disk usage command, and the -a flag says, “Display an entry for each file in a file hierarchy.” Then I use the sort command to sort the du output numerically and in reverse. After that, head -10 shows only the first ten lines of output. In the Music folder on my Mac the command and output look like this:

This is a page from my book, Functional Programming, Simplified

Recursion: How Recursive Scala Function Calls Work

An important point to understand about recursive function calls is that just as they “wind up” as they are called repeatedly, they “unwind” rapidly when the function’s end condition is reached.

In the case of the sum function, the end condition is reached when the Nil element in a List is reached. When sum gets to the Nil element, this pattern of the match expression is matched:

How to use the ‘filter’ method to filter a Scala collection

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 10.17, “How to use filter to Filter a Scala Collection”

Problem

You want to filter the items in a collection to create a new collection that contains only the elements that match your filtering criteria.

The Linux ‘head’ and ‘tail’ commands

Linux head/tail FAQ: Can you share some examples of the Linux head and tail commands?

Sure. The Linux head and tail commands are very similar, so I've included them here together. The head command command prints lines from the beginning of a file (the head), and the tail command prints lines from the end of files. There's one very cool extra thing you can do with the tail command, and I'll show that in the tail example commands below.

Perl: How to extract lines from the middle of a text file

A Perl program to extract lines from the middle of a file

I've always been a big fan of the Unix head and tail commands, but several times I have wanted to print a range of lines from the middle of a text file -- not just the beginning or end of a file. Not liking the available solutions, I wrote my own.

Here is the source code for a program named "extract.pl", which prints lines from a text file beginning at the start line you specify and ending at the stop line.