Ruby modify and add a hash value in array of hashes

Question

I'm trying to modify an array of hashes using collect!. For each hash I want to add 1 new key/value and modify a different key/value. However, I'm having problems modifying the existing hash value using sub!. It seems to completely replace the hash with a single array entry equaling the result of the sub! command

paths = [{:path=>"bin/ruby/file1", :tag=>"v_10"}, {:path=>"usr/name/subdir/file2", :tag=>"v_12"}]

paths.collect! do |x|
  x.merge(Hash[:file => x[:path].sub(/.*\//,"")])  # Grab file name
  x[:path].sub!(/\/\w+$/,"")                       # remove file name from path
end

RESULT:
=> ["bin/ruby", "usr/name/subdir"]

DESIRED RESULT:
=> [{:path=>"bin/ruby", :tag=>"v_10", :file=>"file1"}, {:path=>"usr/name/subdir", :tag=>"v_12", :file=>"file2"}]

user229044 · Accepted Answer · 2014-02-24 02:46:56Z

2

You don't want collect!, you want each. Collect maps the input hash to the output of each block, and the output of your block is the result of your .sub call, meaning you get a flat array of transformed :path values.

You can also just set the key :file directly rather than building a new hash and attempting to merge it:

paths = [{:path=>"bin/ruby/file1", :tag=>"v_10"}, {:path=>"usr/name/subdir/file2", :tag=>"v_12"}]

paths.each do |x|
  x[:file] = x[:path].sub(/.*\//, '')
  x[:path].sub!(/\/\w+$/,"")                       # remove file name from path
end

puts paths.inspect # [{:path=>"bin/ruby", :tag=>"v_10", :file=>"file1"}, {:path=>"usr/name/subdir", :tag=>"v_12", :file=>"file2"}]

edited Feb 24, 2014 at 2:46

answered Feb 24, 2014 at 0:25

user229044♦

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6 Comments

mu is too short Over a year ago

collect! not collect. collect would have been fine (with merge! instead of merge) but a bit pointless

user229044 Over a year ago

@muistooshort Either option would have been wrong, he was returning a single value, x[:path].sub!(/\/\w+$/,"") from the block

Greg Ruhl Over a year ago

meagar, thanks for the explanation as to why my code was not working + the answer. I was under the impression that we could not modify in-place with each (hence the reason for my attempted use of collect). How does creating x[:file] work here? Is it because the array entry is pointing to the Hash and that pointer is not actually changing (so each works)?

user229044 Over a year ago

You're iterating over the array of objects, and each iteration sets x to the next object in the array. Objects are assigned by value in Ruby, so modifying x modifies the object x points to. There is nothing wrong with doing collect when you want to leave the original version of the array intact, but you need to return completely new objects or both arrays will contain references to the same objects.

mu is too short Over a year ago

The only reason the block's return value was relevant at all is that he was using collect!, if he used collect then the block's return value would have been irrelevant. You still have a typo in your answer as your first sentence doesn't make sense.

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Rafa Paez · Accepted Answer · 2014-02-24 01:02:21Z

1

Functional Style Version

paths.map do |path| 
  parts = path[:path].split('/'); 
  { 
    :path => parts.first(parts.length - 1).join('/'), 
    :tag => path[:tag], 
    :file => parts.last
  }
end

answered Feb 24, 2014 at 1:02

Rafa Paez

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