Friday, March 9, 2007

Ruby has a big standard library

One of the aspects of Ruby that I've been most impressed by is the size and sophistication of its standard libraries. There are complete, easy to use classes for almost all of the functionality I've needed to date - and importantly they have the functions one really needs to be productive built right in. A good example of this is code to loop through a directory and operate on certain types of files. After some fishing around the web, I found some bits and pieces of very simple code that does exactly what I need it to do. Now, I am not expert, so I would appreciate critiques and better solutions, as I know that I'm missing ways to do this better, but I've already found a pretty simple way to do this. You'll also probably note that I like long variable names.

The following code is looking through a directory, all the way down to the leafs (file in sub-directories) and returning files that end in "a.dat". This is the extension of the polygon metadata files from the Census website. It then creates the file name for the actual polygon files (they have the same name, without an "a" before the extension) and the metadata files. From here, it passes those into the functions which read, parse these files to generate the KML outpus, which I will share when they are more robust and mature.

Find.find("/Users/xxx/Desktop/Census 2000 CSDs") do |path|
  if path.match("a.dat")

# This returns the file name, minus the second parameter
    filename = File.basename(path, "a.dat")
    path = File.dirname(path)
    polyShapeFilename = path + "/" + filename + ".dat"
    polyDataFilename = path + "/" + filename + "a.dat"
    outputFilename = Dir.getwd + "/batch_outputs/" + filename + ".kml"

    puts "Starting #{filename}"

# I'll publish this method when it is more complete

    puts "Done #{filename}"


An example of productivity I am talking about is the Find class. This built in class recursively searches through directories - how helpful!

One of the most powerful concepts in Ruby that I am just getting comfortable with is the block, like Find.find("/Users/xxx/Desktop/Census 2000 CSDs") do |path| that lets you run loops over collections of things. In this case, the code is going to loop every time the find method returns a path. I'm sure I'm butchering the Ruby language, but if a novice can figure these parts out, then the language, and its authors, have done a number of things right.

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