Note: make sure you are running Ruby version 1.9.3. The command line
ruby --version will tell you which version is currently
installed; if your version is older than 1.9.3, follow the
installation instructions to upgrade.
Cut and paste the following code into a file named squared.rb:
... your code goes here ... puts 9.squared puts 16.squared
Then replace the line at the top with Ruby code that adds a new method
squared to the Numeric class. The method should
return the square of the object on which it is invoked. Once this
method is defined you should be able to use expressions such as
9.squared. Test the code by typing ruby squared.rb
to your shell.
Create a file named sort.rb
that defines a method funny_sort, which takes a single
argument containing an array of strings and returns an array containing
the same strings in sorted order. The sorting of the strings is
determined by the first sequence of digits within each string (sort
numerically, not alphabetically).
For example, the string "abc99.6" is sorted according to the number
99, and "-100x500" is sorted according to the number 100. If a
string contains no decimal digits then
it must be sorted according to -1 (all such strings will appear
first in the output, in any order). In your implementation you must use the
sort function implemented by the Enumerable
module, and you must provide a block that ensures the correct sorting
order. In addition to defining funny_sort your file
sort.rb must include code that invokes
funny_sort a few times and prints the results to
demonstrate that your code works.
Create a file named starts_with.rb
that adds a method each_starts_with, which takes
two arguments plus a block. The first argument is an array of
strings and the second argument is a string. The method
iterates over each of the strings in the array,
invoking the block for each element whose first characters match
the second argument exactly. The matching string is passed to
the block as an argument. Here is an example of an irb
session illustrating how the method should work:
$ irb --simple-prompt
>> load "starts_with.rb"
=> true
>> each_starts_with(["abcd", "axyz", "able", "xyzab", "qrst"], "ab") {|s| puts s}
abcd
able
=> ["abcd", "axyz", "able", "xyzab", "qrst"]
>>
Include code in your starts_with.rb file that invokes
starts_with to demonstrate that it works
correctly.
Create a file named filter.rb
that defines a method filter, which takes one or
two arguments plus a block. The first argument is an array of
numbers and the second argument, if specified, is a hash
containing zero or more options. The method iterates over each
of the numbers in the array, invoking the block with each number
that matches the options. The filter method must
support the following options:
| min | Skip any numbers less than the value of this option. |
| max | Skip any numbers greater than the value of this option. |
| odd | If this option is defined, skip any even numbers. |
| even | If this option is defined, skip any odd numbers. |
| scale | If this option is defined, multiply each number by the value of the option before passing to the block. |
Here is an example of an irb
session illustrating how the method should work:
$ irb --simple-prompt
>> load "filter.rb"
=> true
>> nums = [6, -5, 319, 400, 18, 94, 11]
=> [6, -5, 319, 400, 18, 94, 11]
>> filter(nums, :min => 10, :max => 350, :odd => 1, :scale => 2) {|n| puts n}
638
22
=> nil
>> filter(nums, :max => 0) {|n| puts n}
-5
=> nil
>> filter(nums) {|n| puts n}
6
-5
319
400
18
94
11
=> nil
>>
Include code in your filter.rb file that invokes
filter to demonstrate that it works
correctly. Your solution must use symbols to index into hashes
whereever that is practical. Note: your implementation of
filter need not return nil as in the examples above.
Create a file named group.rb that adds a new method
each_group_by_first_letter to the Enumerable
module. This method is an iterator that yields two items at a time:
a one-letter string and an array of all the input values starting with
that letter. The order in which letters are yielded, and the order of
values in the array, are not important. Once you have defined this
iterator in the Enumerable module, you can use it for
any enumerable collection. For example:
>> x = ["abcd", "axyz", "able", "xyzab", "qrst"]
=> ["abcd", "axyz", "able", "xyzab", "qrst"]
>> x.each_group_by_first_letter do |letter, words|
?> printf("%s: %s\n", letter, words.join(" "));
?> end
a: abcd axyz able
x: xyzab
q: qrst
Include code in your group.rb file that invokes
each_group_by_first_letter to demonstrate that it works
correctly.
Create a file adder.rb that defines a class
Adder. This class should provide a constructor that
takes a single integer argument; other than this, the class should
contain only a single method named method_missing.
As discussed in class, this method will get invoked whenever a
nonexistent method is invoked on objects of this class. If
a method of the form plusnum is invoked, where
num is a positive integer, your code should add a new method
by that name to the Adder class and invoke it; in the future, the
method will already exist
so method_missing will not be invoked. The method
plusnum should return i+num, where i
was the argument passed to the object's constructor. If the method
name doesn't have the form plusnum then your
method_missing method should invoke method_missing
on the superclass so that a proper error gets generated. Note: you may
find the methods class_eval, eval, and
super useful in your solution.
Here is an example irb
session illustrating how the class should work:
$ irb --simple-prompt
>> load "adder.rb"
=> true
>> x = Adder.new(10)
>> x.plus20
=> 30
>> x.plus25
=> 35
>> x.minus2
NoMethodError: undefined method `minus2' for #<Adder:0x2cecca8 @i=10>
from ./adder.rb:15:in `method_missing'
from (irb):6
These points will be awarded if your Ruby code for the problems above is clean and readable.
Array, Hash, and
String at
http://ruby-doc.org/core-1.9.3/.x is the string "abcdef"
then x[1..4] is "bcde".class_eval and instance_eval
can be very confusing; you may find this
explanation helpful in understanding them.
Use the standard class submission mechanism
to submit the code files you created for the problems, including
squared.rb, sort.rb, starts_with.rb,
filter.rb, group.rb, and adder.rb.