Seven in Seven, Ruby Day 2

Here we're starting to get a little deeper into Ruby, coming across a few nice features, such as code blocks (closures) and mixins. Still not really sure what the fuss is about though.

What did I learn?

Ruby is starting to look quite like python. Duck typing can catch you out : a regex pattern looks like a sting, quacks like a string, but doesn't waddle like a string. Ruby has nicked some of Perls' pattern-matching syntax, which is a good thing as it's great for rule-based input processing.

Exercise : Can we translate a hash to an array, and can we iterate over a hash?


Well, yes we can :

#!/usr/bin/ruby

numbers = {1=>'one', 2=> 'two', 3=>'three', 4 => 'four'}
num_array = []

numbers.each do |num, str|
        num_array.push([num,str])
end
p 'My class is ' + num_array.class.to_s
p 'Element class is ' + num_array[0].class.to_s
puts num_array

 Of course we could have just used numbers.flatten()

#!/usr/bin/ruby
=begin
This exercise is to print the numbers 1 to 16 in groups of 4
=end

#Old school
i = 0
ary = []
(1..16).each do |num|
        if i % 4 ==  0
                if i > 0
                        p ary
                end
                ary = []
        end
        ary.push(num)
        i = i + 1
end
p ary

# One liner -using a code block
(1..16).each_slice(4) {|ary| p ary}

Exercise 3 : Populate the Tree class from a hash.

 I'm not going to put all the code up for this, and I struggled a bit to get it going. The solution that I settled on was to have two classes,  a Tree class that took the hash argument which extended a Node class that was the basic structure.

The Node initializer looks like this :

def initialize(name, node = {})
    @children = []
    @node_name = name
    node.each { |key,child| @children.push(Node.new(key,child)) }
  end

So it just build the tree recursively.

Exercise 4 implement grep

=begin
Grep implementation, matches a string against lines from a file,
outputs the line number and contents of the matched line

usage : rb_grep pattern file
=end

i = 1
File.open(ARGV[1],"r") do |f|
        pattern = Regexp.new(ARGV[0])
        while line =  f.gets 
                line =~ pattern and printf("%d : %s", i,line)
                i = i + 1
        end 
end