Category Archives: Programming - Page 2

Convert an integer to a sequence of digits in Xquery

I am new to the functional programming paradigm and Xquery. As part of a larger exercise, I wanted to sum the digits of an integer.  The first part of that problem is to solve the smaller problem: convert an integer to a sequence of integers that I can then pass to fn:sum as a parameter.

(: I've declared the function in the nwnu namespace for testing purposes :)
declare function nwnu:number-to-seq($num as xs:integer)
as xs:integer* {
  if($num gt 9) then
    (
      nwnu:number-to-seq(xs:integer(math:floor($num div 10))),
      xs:integer(math:floor($num mod 10))
    )
  else
    $num
};

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Introduction to web scraping with Node.js

The internet has a wealth of freely available information in difficult to consume formats.  For example, ClicheSite has lists of cliches, euphemisms, and other phrases that are just perfect for a hangman or Wheel of Fortune game.  Coincidentally, I wanted to write such a game to learn some new technologies, so I wrote a short, simple Node.js script to scrape some pages for those phrases.  In this tutorial, I’ll discuss how to make an HTTP request and get a page’s HTML, how to parse the HTML for specific information, and why you would and would not want to do this in the first place.
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Swap object keys and values in Javascript

There are times when I would like to do work with the values in a Javascript object used as a hash map.  For example, sometimes I’d like to iterate over the values and perform an action on them, or perhaps check that a value exists in the hash map.  In this post, I’ll write a function that inverts the keys and values in a hash map, give a couple of examples in regards to how and why you’d want to do that, and explain the short-comings of the approach.

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Introduction to memoization with Javascript

Memoization is a function optimization technique used to avoid remaking calculations in subsequent function calls.  The classic example, which we’ll demonstrate here, is the factorial function.  5! = 5 * 4 * 3 * 2 * 1… factorials are recursive in nature if we give it some thought.  5! = 5 * 4! and 4! = 4 * 3! and so on.  By recognizing this pattern, we can also recognize that if we calculate 5! and save the results, then we should not have to recalculate it when we do 7!.  Instead of calculating 7! by 7 * 6 * 5 * 4 * 3 * 2 * 1, we’ll calculate it by 7 * 6 * 5!.

We’ll first examine the naive approach and then the memoization method.  All in Javascript, and all with code samples…
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Maintain a running list of your external IP address

At home, I have a consumer level cable internet service.  I actually do not know if I have a dynamic IP address or a static IP address because I haven’t really cared enough to ask my ISP.  I would assume that I have a dynamic IP address since most ISPs charge a premium for a static IP address, but since I don’t know for sure I thought I would find out for myself.

Using http://whatismyip.com ‘s “automation” page, Perl, and cron, I am going to maintain a list of my external IP addresses.  Not only will this answer the original question, but I can also gather some additional information, such as how often my IP address changes and whether or not I can force my IP address to change by disconnecting my modem :).

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Fixing line breaks in HL7 messages in Mirth Connect

Anyone who has worked in the world of healthcare integration or with HL7 knows that if you have seen one HL7 message, you’ve seen one HL7 message.  Now, a common problem with some source systems is that a line break will sneak in the middle of a segment, rendering the whole message invalid.  How many times have you seen this message?

MSH|^~\&|DDTEK LAB|ELAB-1|DDTEK OE|BLDG14|200502150930||ORU^R01^ORU_R01|CTRL-9876|P|2.4
PID|||010-11-1111||Estherhaus^Eva^E^^^^L|Smith|19720520|F|||256 Sherwood Forest Dr.^^Baton Rouge^LA^70809||(225)334-5232|(225)752-1213||||AC010111111||76-B4335^LA^20070520
OBR|1|948642^DDTEK OE|917363^DDTEK LAB|1554-5^GLUCOSE|||200502150730|||||||||020-22-2222^Levin-Epstein^Anna^^^^MD^^Micro-Managed
Health Associates|||||||||F|||||||030-33-3333&Honeywell&Carson&&&&MD
OBX|1|SN|1554-5^GLUCOSE^^^POST 12H CFST:MCNC:PT:SER/PLAS:QN||^175|mg/dl|70_105|H|||F

Notice the “Health Associates” segment? Obviously, this segment invalidates the message.  When this message is sent through a Mirth channel that expects incoming HL7, the message will error out when Mirth tries to parse it.  Here is how we can fix that.

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Zip code library in CodeIgniter

Recently, a client wanted a member search for his website that included a search by zip code. The ‘easy’ solution would be to implement the search as a LIKE statement in SQL, but the solution is inaccurate, and I like the ‘good’ solutions over the ‘easy’ ones. I looked for a CodeIgniter library that would give me the functionality for which I wanted to implement, but no such thing existed. Then, I came across Micah Carrick’s native PHP library which gave the exact functionality I was looking for. I did end up using his library, but not without modification: I’ve ported the native library to a CodeIgniter library. This is where you can get it.

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“Presto” math trick in Java

According to Futility Closet, if you start with a 3 digit and place it next to the same number to form a 6 digit number, you can divide the 6 digit number by 7, 11, and then 13 and you will end up with the original 3 digit number and no remainders. For example, by taking the number 412 and making it 412412 and then doing the divisions, you will end up with 412. I wrote a small program in Java to test it.

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jQuery change event on checkbox

A lot of times, you’ll want to call a javascript function when a checkbox is changed from unchecked to check and vice versa. Up until the release of jQuery 1.4, the obvious way to do it (the jQuery .change() event) did not work properly across all versions of Internet Explorer. Instead, you had to check for the .click() event. This was an accessibility problem because it did not fire when a user changed a checkbox with the space bar instead of by clicking. Well, now we can rejoice. The following code snippet works exactly how you think it would across browsers, including IE.

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Recursive Collatz conjecture in PHP

I stumbled across a blog post by Brie Gordon about the Collatz conjecture, so naturally I had to Wikipedia it. The simple story is that for any given integer, if it is even you divide it by 2 and if it is odd you multiply it by 3 and add 1. You continue this pattern with the returned numbers, and eventually the number will reach 1. So, to kill some time, I wrote a recursive version in PHP.  Here it is:

function collatz($num)
{   
  if($num == 1)
  {
    echo "<p style='color: red'>" . $num . "</p>\n";
    return;
  }

  if($num % 2 == 0) //even
  {
    echo "<p style='color: green'>" . $num . "</p>\n";
    return collatz($num / 2);
  }
  else
  {
    echo "<p style='color: red'>" . $num . "</p>\n";
    return collatz(3 * $num + 1);
  }
}