From: "Aaron D. Gifford" <astounding@...>
Date: 2010-02-15T16:08:30+09:00
Subject: Re: Compare and delete element from an array

On Sun, Feb 14, 2010 at 10:48 PM, Greg Ma <gregorylepacha@msn.com> wrote:
>
>> Note that the first version with a "puts" at the end of the delete_if
>> block failed to remove element "two", but reordering the operation in
>> the second version worked.
>>
> Even if i remove the puts, it still doesnt remove anything.
>
>  def remove_tags(array_of_tags)
>    if !array_of_tags.empty?
>      array_of_tags.each do |tag|
>        tags.delete_if { |x| x.name == tag }
>      end
>    end
>  end

You call the "delete_if()" method on the "tags" variable--where is
tags defined?  You've fixed one bug (and it was indeed a bug). If your
code isn't working now, it likely has to do with the scope where tags
is defined.  In your original post you didn't mention getting a
NameError "undefined local variable or method `tags'" exception, so
unless your code (or whatever code executes your code) rescues such an
exception silently, I assume that "tags" IS in fact defined
somehow/somewhere.

Since I don't know how your "tags" array or Student class works, I
contrived something that's probably very, very different, but may give
you an idea where to look in your own code for your bug:

### CODE STARTS ###

class Tag
  def initialize(name)
    @name = name
  end
  attr_accessor :name

  def to_s
    "TAG(#{@name})"
  end
end

class Student
  def initialize()
    @tag_list = []
  end

  ## Add a single tag to the Student:
  def add_tags(array_of_tags)
    array_of_tags.each do |tag_name|
      @tag_list << Tag.new(tag_name)
    end
  end

  ## Remove multiple tags from the Student:
  def remove_tags(array_of_tags)
    array_of_tags.each do |tag_name|
      @tag_list.delete_if { |x| x.name == tag_name }
    end
  end

  def to_s
    "STUDENT(" + @tag_list.map{ |tag| tag.to_s }.join(",") + ")"
  end
end

jane_doe = Student.new
jane_doe.add_tags(["intelligent", "lazy", "geek", "irresponsible",
"nerd", "smart"])

puts "Jane has these tags:"
puts jane_doe.to_s

tags_to_remove = [ "lazy", "irresponsible" ]

puts "Removing tags with these names:"
puts "  " + tags_to_remove.join(",")

## Remove the tags:
jane_doe.remove_tags(tags_to_remove)

puts "After removal, Jane has these tags:"
puts jane_doe.to_s

### CODE ENDS ###

### SAMPLE OUTPUT: ###
Jane has these tags:
STUDENT(TAG(intelligent),TAG(lazy),TAG(geek),TAG(irresponsible),TAG(nerd),TAG(smart))
Removing tags with these names:
  lazy,irresponsible
After removal, Jane has these tags:
STUDENT(TAG(intelligent),TAG(geek),TAG(nerd),TAG(smart))
### OUTPUT ENDS ###

In the above contrived sample, notice that the Student#remove_tags()
method is a bit different than your method.  That's because I defined
the equiv. of your "tags" variable as a Student class instance
variable "@tag_list" instead.  Also I omitted the "if" statement "if
!@tag_list.empty?" (or "if !tags.empty?" in your code) because the
each method will not execute the block at all if the array is empty to
begin with--it's redundant and not needed.

I hope this gives you an idea of where in your own code to look to debug it.

Aaron out.