Manipulate hash in Ruby

Question

I have a hash that looks like

{
 "lt"=>"456",
 "c"=>"123",
 "system"=>{"pl"=>"valid-player-name", "plv"=>"player_version_1"},
 "usage"=>{"trace"=>"1", "cq"=>"versionid", "stream"=>"od", 
 "uid"=>"9", "pst"=>[["0", "1", "10"]], "dur"=>"0", "vt"=>"2"}
}

How can I go about turning it into a hash that looks like

{
 "lt"=>"456",
 "c"=>"123",
 "pl"=>"valid-player-name", 
 "plv"=>"player_version_1",
 "trace"=>"1", 
 "cq"=>"versionid", 
 "stream"=>"od", 
 "uid"=>"9", 
 "pst"=>[["0", "1", "10"]], "dur"=>"0", "vt"=>"2"
}

I basically want to get rid of the keys system and usage and keep what's nested inside them

Just to mention, there's an } additional in your expected ouput. — Sebastián Palma
– Sebastián Palma, Commented Jun 27, 2017 at 14:20

Sergio Tulentsev · Accepted Answer · 2017-06-27 14:25:35Z

2

"Low-tech" version :)

h = { ... }
h.merge!(h.delete('system'))
h.merge!(h.delete('usage'))

answered Jun 27, 2017 at 14:25

Sergio Tulentsev

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2 Comments

Richlewis Over a year ago

Thanks Sergio, always love a low tech version :-), i thought delete would have deleted the whole nested hash, should have tried harder :-(

Richlewis Over a year ago

I know, let myself down a bit there really, thanks for the help

ndnenkov · Accepted Answer · 2017-06-27 14:29:04Z

1

Assuming no rails:

hash.reject { |key, _| %w(system usage).include? key }.merge(hash['system']).merge(hash['usage'])

With active support:

hash.except('system', 'usage').merge(hash['system']).merge(hash['usage'])

edited Jun 27, 2017 at 14:29

answered Jun 27, 2017 at 14:23

ndnenkov

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Comments

Casper · Accepted Answer · 2017-06-27 14:34:24Z

1

A more generic version.

Merge any key that contains a hash:

h = { ... }

hnew = h.inject(h.dup) { |h2, (k, v)|
  h2.merge!(h2.delete(k)) if v.is_a?(Hash)
  h2
}

answered Jun 27, 2017 at 14:34

Casper

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Comments

David Grayson · Accepted Answer · 2017-06-27 14:38:42Z

Assuming that your data has the same structure each time, I might opt for something simple and easy to understand like this:

def manipulate_hash(h)
  {
    "lt" => h["lt"],
    "c" => h["c"],
    "pl" => h["system"]["pl"],
    "plv" => h["system"]["plv"],
    "trace" => h["usage"]["trace"],
    "cq" => h["usage"]["cq"],
    "stream" => h["usage"]["stream"],
    "uid" => h["uid"],
    "pst" => h["pst"],
    "dur" => h["dur"],
    "vt" => h["vt"]
  }
end

I chose to make the hash using one big hash literal expression that spans multiple lines. If you don't like that, you could build it up on multiple lines like this:

def manipulate_hash
  r = {}
  r["lt"] = h["lt"]
  r["c"] = h["c"]
  ...
  r
end

You might consider using fetch instead of the [] angle brackets. That way, you'll get an exception if the expected key is missing from the hash. For example, replace h["lt"] with h.fetch("lt").

eiko · Accepted Answer · 2017-06-27 14:36:27Z

0

If you plan to have an arbitrarily large list of keys to merge, this is an easily scaleable method:

["system", "usage"].each_with_object(myhash) do |key|
  myhash.merge!(myhash.delete(key))
end

edited Jun 27, 2017 at 14:36

answered Jun 27, 2017 at 14:23

eiko

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