From: "Aaron D. Gifford" <astounding@...>
Date: 2010-02-15T09:50:56+09:00
Subject: Re: Compare and delete element from an array

On Sun, Feb 14, 2010 at 4:45 PM, Greg Ma <gregorylepacha@msn.com> wrote:
> def remove_tags(array_of_tags)
>    if !array_of_tags.empty?
>      array_of_tags.each do |tag|
>        tags.delete_if {
>          |x| x.name == tag
>          puts x.name + "-"+ x.name.length.to_s
>          puts tag + "-"+ tag.length.to_s
>          puts "-----"
>          }
>      end
>      puts tags
>    end
>  end

Move the line:

  x.name == tag

to the end of the block:

def remove_tags(array_of_tags)
  if !array_of_tags.empty?
    array_of_tags.each do |tag|
      tags.delete_if  {|x|
        puts x.name + "-"+ x.name.length.to_s
        puts tag + "-"+ tag.length.to_s
        puts "-----"
        x.name == tag
      }
    end
    puts tags
  end
end

The Array#delete_if() method only removes array elements IF the block
evaluates to true. With the "x.name == tag" test positioned at the
beginning of the block, it is effectively ignored, since the last
expression in the block will be the block's return value.  You were
returning whatever the 'puts "-----"' method returns--nil in this
case, which is considered "false" and so no elements would ever be
deleted.  By moving the "x.name == tag" expression to the bottom of
the block, you will return a boolean result of the comparison.

Here's another example of this behavior:
irb(main):001:0> ["one", "two", "three", "four", "five"].delete_if{|x|
x=="two";puts x}
one
two
three
four
five
=> ["one", "two", "three", "four", "five"]
irb(main):002:0> ["one", "two", "three", "four", "five"].delete_if{|x|
puts x;x=="two"}
one
two
three
four
five
=> ["one", "three", "four", "five"]

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.

Aaron out.