Date/time programming is one of the tricky aspects of software development. Although inherently not complex in itself, coding date/time algorithms can be a subtle source of bugs. Especially in web development a feature such as payment subscription processing that ranges from days to weeks to months can get complex quickly. Also such kind of scenarios require additional features like auto renewal, scheduled email alerts to subscribers etc. Such kind of features require good date/time handling algorithms and libraries that handle such chores are always welcome.
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algorithms
Splitting a text on word boundaries
Substring extraction of a long piece of text is a common element in web design, mostly in blogs and other CMS for displaying excerpts. The most common way to show an excerpt is to get n number of characters of the text, or n number of words. We will explore both ways. In PHP we frequently use the substr function. However, substr or any of its variants does not split the text at word boundaries, keeping broken words hanging at the end. There are many ways we can prevent this, using some text adjustments. A simple one is shown here.
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Building a adjacency matrix of a graph
In the last post we constructed a graph structure using the Structure_Graph Pear library. But building a graph is not enough; we also need the ability to search through it. To make it easier to build search algorithms, it is useful if we can represent the graph and its connections in a different way; adjacency matrix being one such representation.
Building a Graph data structure in PHP
Graphs are one of the most frequently used data structures,along with linked lists and trees. In a recent PHP project I needed to build a Graph structure to analyze some interlinked urls. The problem was of a simple nature, so rather than writing my own code, I went with the one available in the Pear repository.
The Pear Structures_Graph package allows creating and manipulating graph data structures. It allows building of either directed or undirected graphs, with data and metadata stored in nodes. The library provides functions for graph traversing as well as for characteristic extraction from the graph topology.
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Face detection in images using PHP
In a previous post we saw how to detect human faces in images using JavaScript. In the current post we will look into a PHP port of a JavaScript face detection algorithm without using openCV. Since the code is completed written in PHP it cannot attain the raw speed that C,C++ provides, but for many trivial application a PHP version can do.
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Generating a color palette from a image in php
In the previous post we saw how we can generate a screenshot from a url. In this post we will see how we can create a color palette of the screenshot (or any other image for that matter) using PHP and GD. This can be useful if you need to quickly get the color scheme of a website or a image. Below are a few example images and their palettes generated using the program.
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Sorting PHP arrays with substrings
A couple of days back I encountered the following request on a forum for sorting a single dimensional array. The programmer wanted to sort the following array by the substring after the colon. For example ‘CDF’ in the string ‘66345:CDF’. Those values that do not have any colon should be ignored and pushed to the end of the array. Also, the length of the strings are not constant.
$values = array("66345:CDF", "61179:HGT", "64146:ABA", "68768:BNG", "68015:ZCZ", "80231:LPO", "64146:QWP", "68736:HHB", "86801:MNV", "80178:OIU", "80178:ASE", "88178:BRT", "801782OIU", "801378ASE", "881578BRT"); |
Generating UPC check digit
The following small code generates check digit for UPC-A codes. You can use it for example to generate random UPC-A codes.
Check digit calculation
The check digit is calculated as follows:
1. Add the digits in the odd-numbered positions together and multiply by three.
2. Add the digits in the even-numbered positions to the above result.
3. Find the result modulo 10 (i.e. the remainder when the result is divided by 10).
4. If the result is not zero, subtract the result from ten.
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Porter Stemming algorithm for search
In this post we will see how to use a Stemming algorithm for search purposes.
A stemming algorithm lets you reduce each English input word to its basic root or stem (e.g. ‘walking’ to ‘walk’) so that variations on a word (‘walks’, ‘walked’, ‘walking’) are considered equivalent when searching. This stems can than be used in a search query rather than the original words, which generally (but not always) results in more relevant search results. The main use of stemming is in keyword indexing for search. For example if you have a article or document titled ‘blogging tips for late workers‘ and you run it through the algorithm you will get a list of stems for the title – blog, tip, late, worker; under which you can than index the article or document.
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