Replace values in hash

ruby-talk
1

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?

···

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Posted via http://www.ruby-forum.com/.

2

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/Enumerable.html#M000429

7.

···

On Nov 5, 1:53 am, Jason Lillywhite <jason.lillywh...@gmail.com> wrote:

how would I iterate over a hash, such as

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

3

h.keys.each {|d| h[d] = "foo" if h[d] == nil}

···

-----Original Message-----
From: jason.lillywhite@gmail.com [mailto:jason.lillywhite@gmail.com]
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"}

4

Jason Lillywhite <jason.lillywhite@gmail.com> 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"}

···

--
Brian Adkins
http://www.lojic.com/

5

Thank you!

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

am I missing something?

···

--
Posted via http://www.ruby-forum.com/.

6

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

···

On Wed, Nov 5, 2008 at 12:38 PM, Brian Adkins <lojicdotcom@gmail.com> wrote:

Jason Lillywhite <jason.lillywhite@gmail.com> 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"}

--
Brian Adkins
http://www.lojic.com/
Lojic Technologies Blog

7

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

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

T.

···

On Nov 5, 2:54 am, Jason Lillywhite <jason.lillywh...@gmail.com> wrote:

Thank you!

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

am I missing something?

8

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.

···

On Nov 5, 10:31 am, Trans <transf...@gmail.com> wrote:

On Nov 5, 2:54 am, Jason Lillywhite <jason.lillywh...@gmail.com> > 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?