Forum: Ruby replace values in hash

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Jason L. (Guest)
on 2008-11-05 08:55
how would I iterate over a hash, such as

x = { 'a' => "hi", 'b' => nil, 'c' => "do"}

and replace nil values with 'foo' then return the hash again?
Thomas S. (Guest)
on 2008-11-05 09:41
(Received via mailing list)
On Nov 5, 1:53 am, Jason L. <removed_email_address@domain.invalid>
wrote:
> how would I iterate over a hash, such as
>
> x = { 'a' => "hi", 'b' => nil, 'c' => "do"}

  x.each{ |k,v| x[k] = 'foo' unless v }

However, it is not always sane to alter something while you are
iterating over it. So,

  h = {}
  x.each{ |k,v| h[k] = v.nil? ? v : 'foo' }
  x.replace(h)

Or use Facets Enumerable#mash (alias #graph)

  require 'facets/enumerable/mash'

  x = x.mash{ |k,v| [k, v.nil? ? v : 'foo'] }

http://facets.rubyforge.org/doc/api/core/classes/E...

7.
Jason L. (Guest)
on 2008-11-05 09:56
Thank you!

However, I am getting undefined method 'mash' even though I do require
'facets/enumerable/mash'

am I missing something?
Jason L. (Guest)
on 2008-11-05 10:23
I guess since Enumerable is a Module, I need to do

include Enumerable... Thanks for the solution!
Sarcar, Shourya C (GE Healthcare) (Guest)
on 2008-11-05 12:54
(Received via mailing list)
> -----Original Message-----
> From: removed_email_address@domain.invalid [mailto:removed_email_address@domain.invalid]
> Sent: Wednesday, November 05, 2008 12:24 PM
> To: ruby-talk ML
> Subject: replace values in hash
>
> how would I iterate over a hash, such as
>
> x = { 'a' => "hi", 'b' => nil, 'c' => "do"}


 h.keys.each {|d| h[d] = "foo" if h[d] == nil}
Thomas S. (Guest)
on 2008-11-05 17:33
(Received via mailing list)
On Nov 5, 2:54 am, Jason L. <removed_email_address@domain.invalid>
wrote:
> Thank you!
>
> However, I am getting undefined method 'mash' even though I do require
> 'facets/enumerable/mash'
>
> am I missing something?

Don't think so. It's working fine for me.

What version of Ruby and Facets and what platform are you running?

T.
Brian A. (Guest)
on 2008-11-05 19:40
(Received via mailing list)
Jason L. <removed_email_address@domain.invalid> writes:

> how would I iterate over a hash, such as
>
> x = { 'a' => "hi", 'b' => nil, 'c' => "do"}
>
> and replace nil values with 'foo' then return the hash again?

~/temp$ cat -b temp.rb
     1  require 'pp'

     2  class Hash
     3    def replace_value old, new
     4      self.inject({}) do |result,pair|
     5        k, v = pair[0], pair[1]
     6        result[k] = (v == old) ? new : v
     7        result
     8      end
     9    end
    10  end

    11  x = { 'a' => "hi", 'b' => nil, 'c' => "do", :d => nil }
    12  pp x
    13  y = x.replace_value(nil, 'foo')
    14  pp y
~/temp$ ruby temp.rb
{"a"=>"hi", "b"=>nil, :d=>nil, "c"=>"do"}
{"a"=>"hi", "b"=>"foo", "c"=>"do", :d=>"foo"}
Thomas S. (Guest)
on 2008-11-05 20:13
(Received via mailing list)
On Nov 5, 10:31 am, Trans <removed_email_address@domain.invalid> wrote:
> Don't think so. It's working fine for me.
>
> What version of Ruby and Facets and what platform are you running?

For anyone who is interested, here's the definition (and some side
notes about how it evolved).

  def mash(&yld)
    if yld
      inject({}) do |h, *kv| # Used to be inject({}) do |h,kv|
        r = *yld[*kv]        # The *-op works different from to_a on
single element hash!!!
        nk, nv = *r          # Used to be nk, nv =
*yld[*kv].to_a.flatten
        h[nk] = nv
        h
      end
    else
      Enumerator.new(self,:mash)  # Used to be Hash[*self.to_a]
    end
  end

T.
James H. (Guest)
on 2008-11-10 16:37
(Received via mailing list)
Not bad. Let's tighten it up a little:

class Hash
  def replace_value(old, new)
    self.inject({}) do |result, (key, existing_value)|
      result[key] = (value == old) ? new : existing_value
      result
    end
  end
end

This isn't bad, but you wouldn't want to do this for large Hashes since
you
end up copying the original.

James
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