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Given an array of hashes, I want to create a method that returns a hash where the keys are the unique values of the hashes in the array.
For example, I'd like to take
[
{foo: 'bar', baz: 'bang'},
{foo: 'rab', baz: 'bang'},
{foo: 'bizz', baz: 'buzz'}
]
and return
{
foo: ['bar', 'rab', 'bizz'],
baz: ['bang', 'buzz']
}
I am currently accomplishing this using:
def my_fantastic_method(data)
response_data = { foo: [], baz: []}
data.each { |data|
data.attributes.each { |key, value|
response_data[key.to_sym] << value
}
}
response_data.each { |key, value| response_data[key] = response_data[key].uniq }
response_data
end
Is there a more elegant way of doing this? Thanks!
Your current approach is already pretty good; I don't see much room for improvement. I would write it like this:
def my_fantastic_method(data_list)
data_list.each_with_object(Hash.new { |h, k| h[k] = Set.new }) do |data, result|
data.attributes.each do |key, value|
result[key.to_sym] << value
end
end
end
By setting a default value on each hash value, I have eliminated the need to explicitly declare foo: [], bar: [].
By using each_with_object, I have eliminated the need to declare a local variable and explicitly return it at the end.
By using Set, there is no need to call uniq on the final result. This requires less code, and is more performant. However, if you really want the final result to be a mapping to Arrays rather than Sets, then you would need to call to_a on each value at the end of the method.
I have used different variable names for data_list and data. Call these whatever you like, but it's typically considered bad practice to shadow outer variables.
Here are a couple of one-liners. (I'm pretty sure #eiko was being facetious, but I'm proving him correct)
This one reads well and is easy to follow (caveat: requires Ruby 2.4+ for transform_values):
array.flat_map(&:entries).group_by(&:first).transform_values{|v| v.map(&:last).uniq}
Here's another, using the block form of merge to specify an alternate merge method, which in this case is combining the values into a uniq array:
array.reduce{|h, el| h.merge(el){|k, old, new| ([old]+[new]).flatten.uniq}}
You already have a pretty good answer, but I felt golfy and so here is a shorter one:
def the_combiner(a)
hash = {}
a.map(&:to_a).flatten(1).each do |k,v|
hash[k] ||= []
hash[k].push(v)
end
hash
end
Try this:
array.flat_map(&:entries)
.group_by(&:first)
.map{|k,v| {k => v.map(&:last)} }
OR
a.inject({}) {|old_h, new_h|
new_h.each_pair {|k, v|
old_h.key?(k) ? old_h[k] << v : old_h[k]=[v]};
old_h}
If, as in the example, all hashes have the same keys, you could do as follows.
arr = [{ foo: 'bar', baz: 'bang' },
{ foo: 'rab', baz: 'bang' },
{ foo: 'bizz', baz: 'buzz' }]
keys = arr.first.keys
keys.zip(arr.map { |h| h.values_at(*keys) }.transpose.map(&:uniq)).to_h
#=> {:foo=>["bar", "rab", "bizz"], :baz=>["bang", "buzz"]}
The steps are as follows.
keys = arr.first.keys
#=> [:foo, :baz]
a = arr.map { |h| h.values_at(*keys) }
#=> [["bar", "bang"], ["rab", "bang"], ["bizz", "buzz"]]
b = a.transpose
#=> [["bar", "rab", "bizz"], ["bang", "bang", "buzz"]]
c = b.map(&:uniq)
#=> [["bar", "rab", "bizz"], ["bang", "buzz"]]
d = c.to_h
#=> <array of hashes shown above>
I am creating a regex matcher using:
Regexp.new(Regexp.union(some_hash.keys))
is it possible to add a boundaries filter to each element of the array so I have:
/\bkey1\b|\bkey2\b|,....../
For regexp keys:
Regexp.union(some_hash.keys.map { |k| /\b#{k}\b/ })
or for literal keys:
Regexp.union(some_hash.keys.map { |k| /\b#{Regexp.escape(k)}\b/ })
The result of Regexp.union is already a Regexp, no need for Regexp.new. In fact, we can also use plain strings inside Regexp.union, the difference being we don't initialise the flags in each subexpression:
Regexp.union(some_hash.keys.map { |k| "\\b#{k}\\b" })
Regexp.union(some_hash.keys.map { |k| "\\b#{Regexp.escape(k)}\\b" })
You can generate regex in simplest way without using Regexp as
hash = {'a' => 1, 'b' => 2, 'c' => 3, 'd' => 4}
/\b#{hash.keys.join('\b|\b')}\b/
=>/\ba\b|\bb\b|\bc\b|\bd\b/
Not exactly but you can use the scan method ...
for example:-
a = "cruel world"
a.scan(/\w+/) #=> ["cruel", "world"]
a.scan(/.../) #=> ["cru", "el ", "wor"]
a.scan(/(...)/) #=> [["cru"], ["el "], ["wor"]]
a.scan(/(..)(..)/) #=> [["cr", "ue"], ["l ", "wo"]]
I'm having the following hash:
hash = {
"Jason_1" => 2,
"Jason_2" => 3,
"Allison" => 1,
"Jason_3" => 1,
"Michelle" => 1
}
How can I obtain the values of the key starting with "Jason"? Can anyone help me?
Here are a one liners:
# returns a hash with the elements
hash.select { |e| e.start_with? 'Jason' }
# if you want only keys
hash.select { |e| e.start_with? 'Jason' }.keys
# if you want only values
hash.select { |e| e.start_with? 'Jason' }.values
Yet another way:
hash.map { |key, value| key =~ /\AJason/ && value }.compact
Another way with regexp:
hash.select { |x| x =~ /^Jason/ }.values
Another way using scan and find_all method:
Hash[hash.find_all { |key, val| not key.scan(/^Jason/).empty? }]
If you are working in rails this should also work fine:
hash.slice(*hash.keys.grep(/^Jason/))
You can do this in a efficient way and in a single line:
hash.select{|s,v| s =~ /^Jason_/}
I have a condition that gets a hash.
hash = {"_id"=>"4de7140772f8be03da000018", .....}
Yet, I want to rename the key of that hash as follows.
hash = {"id"=>"4de7140772f8be03da000018", ......}
P.S. I don't know what keys are in the hash; they are random. Some keys are prefixed with an underscore that I would like to remove.
hash[:new_key] = hash.delete :old_key
rails Hash has standard method for it:
hash.transform_keys{ |key| key.to_s.upcase }
http://api.rubyonrails.org/classes/Hash.html#method-i-transform_keys
UPD: ruby 2.5 method
If all the keys are strings and all of them have the underscore prefix, then you can patch up the hash in place with this:
h.keys.each { |k| h[k[1, k.length - 1]] = h[k]; h.delete(k) }
The k[1, k.length - 1] bit grabs all of k except the first character. If you want a copy, then:
new_h = Hash[h.map { |k, v| [k[1, k.length - 1], v] }]
Or
new_h = h.inject({ }) { |x, (k,v)| x[k[1, k.length - 1]] = v; x }
You could also use sub if you don't like the k[] notation for extracting a substring:
h.keys.each { |k| h[k.sub(/\A_/, '')] = h[k]; h.delete(k) }
Hash[h.map { |k, v| [k.sub(/\A_/, ''), v] }]
h.inject({ }) { |x, (k,v)| x[k.sub(/\A_/, '')] = v; x }
And, if only some of the keys have the underscore prefix:
h.keys.each do |k|
if(k[0,1] == '_')
h[k[1, k.length - 1]] = h[k]
h.delete(k)
end
end
Similar modifications can be done to all the other variants above but these two:
Hash[h.map { |k, v| [k.sub(/\A_/, ''), v] }]
h.inject({ }) { |x, (k,v)| x[k.sub(/\A_/, '')] = v; x }
should be okay with keys that don't have underscore prefixes without extra modifications.
you can do
hash.inject({}){|option, (k,v) | option["id"] = v if k == "_id"; option}
This should work for your case!
If we want to rename a specific key in hash then we can do it as follows:
Suppose my hash is my_hash = {'test' => 'ruby hash demo'}
Now I want to replace 'test' by 'message', then:
my_hash['message'] = my_hash.delete('test')
For Ruby 2.5 or newer with transform_keys and delete_prefix / delete_suffix methods:
hash1 = { '_id' => 'random1' }
hash2 = { 'old_first' => '123456', 'old_second' => '234567' }
hash3 = { 'first_com' => 'google.com', 'second_com' => 'amazon.com' }
hash1.transform_keys { |key| key.delete_prefix('_') }
# => {"id"=>"random1"}
hash2.transform_keys { |key| key.delete_prefix('old_') }
# => {"first"=>"123456", "second"=>"234567"}
hash3.transform_keys { |key| key.delete_suffix('_com') }
# => {"first"=>"google.com", "second"=>"amazon.com"}
h.inject({}) { |m, (k,v)| m[k.sub(/^_/,'')] = v; m }
hash.each {|k,v| hash.delete(k) && hash[k[1..-1]]=v if k[0,1] == '_'}
I went overkill and came up with the following. My motivation behind this was to append to hash keys to avoid scope conflicts when merging together/flattening hashes.
Examples
Extend Hash Class
Adds rekey method to Hash instances.
# Adds additional methods to Hash
class ::Hash
# Changes the keys on a hash
# Takes a block that passes the current key
# Whatever the block returns becomes the new key
# If a hash is returned for the key it will merge the current hash
# with the returned hash from the block. This allows for nested rekeying.
def rekey
self.each_with_object({}) do |(key, value), previous|
new_key = yield(key, value)
if new_key.is_a?(Hash)
previous.merge!(new_key)
else
previous[new_key] = value
end
end
end
end
Prepend Example
my_feelings_about_icecreams = {
vanilla: 'Delicious',
chocolate: 'Too Chocolatey',
strawberry: 'It Is Alright...'
}
my_feelings_about_icecreams.rekey { |key| "#{key}_icecream".to_sym }
# => {:vanilla_icecream=>"Delicious", :chocolate_icecream=>"Too Chocolatey", :strawberry_icecream=>"It Is Alright..."}
Trim Example
{ _id: 1, ___something_: 'what?!' }.rekey do |key|
trimmed = key.to_s.tr('_', '')
trimmed.to_sym
end
# => {:id=>1, :something=>"what?!"}
Flattening and Appending a "Scope"
If you pass a hash back to rekey it will merge the hash which allows you to flatten collections. This allows us to add scope to our keys when flattening a hash to avoid overwriting a key upon merging.
people = {
bob: {
name: 'Bob',
toys: [
{ what: 'car', color: 'red' },
{ what: 'ball', color: 'blue' }
]
},
tom: {
name: 'Tom',
toys: [
{ what: 'house', color: 'blue; da ba dee da ba die' },
{ what: 'nerf gun', color: 'metallic' }
]
}
}
people.rekey do |person, person_info|
person_info.rekey do |key|
"#{person}_#{key}".to_sym
end
end
# =>
# {
# :bob_name=>"Bob",
# :bob_toys=>[
# {:what=>"car", :color=>"red"},
# {:what=>"ball", :color=>"blue"}
# ],
# :tom_name=>"Tom",
# :tom_toys=>[
# {:what=>"house", :color=>"blue; da ba dee da ba die"},
# {:what=>"nerf gun", :color=>"metallic"}
# ]
# }
Previous answers are good enough, but they might update original data.
In case if you don't want the original data to be affected, you can try my code.
newhash=hash.reject{|k| k=='_id'}.merge({id:hash['_id']})
First it will ignore the key '_id' then merge with the updated one.
Answering exactly what was asked:
hash = {"_id"=>"4de7140772f8be03da000018"}
hash.transform_keys { |key| key[1..] }
# => {"id"=>"4de7140772f8be03da000018"}
The method transform_keys exists in the Hash class since Ruby version 2.5.
https://blog.bigbinary.com/2018/01/09/ruby-2-5-adds-hash-transform_keys-method.html
If you had a hash inside a hash, something like
hash = {
"object" => {
"_id"=>"4de7140772f8be03da000018"
}
}
and if you wanted to change "_id" to something like"token"
you can use deep_transform_keys here and do it like so
hash.deep_transform_keys do |key|
key = "token" if key == "_id"
key
end
which results in
{
"object" => {
"token"=>"4de7140772f8be03da000018"
}
}
Even if you had a symbol key hash instead to start with, something like
hash = {
object: {
id: "4de7140772f8be03da000018"
}
}
you can combine all of these concepts to convert them into a string key hash
hash.deep_transform_keys do |key|
key = "token" if key == :id
key.to_s
end
If you only want to change only one key, there is a straightforward way to do it in Ruby 2.8+ using the transform_keys method. In this example, if you want to change _id to id, then you can:
hash.transform_keys({_id: :id})
Reference: https://bugs.ruby-lang.org/issues/16274
I am wondering what is the best way to convert a json formatted key value pair to ruby hash with symbol as key:
example:
{ 'user': { 'name': 'foo', 'age': 40, 'location': { 'city' : 'bar', 'state': 'ca' } } }
==>
{ :user=>{ :name => 'foo', :age =>'40', :location=>{ :city => 'bar', :state=>'ca' } } }
Is there a helper method can do this?
using the json gem when parsing the json string you can pass in the symbolize_names option. See here: http://flori.github.com/json/doc/index.html (look under parse)
eg:
>> s ="{\"akey\":\"one\",\"bkey\":\"two\"}"
>> JSON.parse(s,:symbolize_names => true)
=> {:akey=>"one", :bkey=>"two"}
Leventix, thank you for your answer.
The Marshal.load(Marshal.dump(h)) method probably has the most integrity of the various methods because it preserves the original key types recursively.
This is important in case you have a nested hash with a mix of string and symbol keys and you want to preserve that mix upon decode (for instance, this could happen if your hash contains your own custom objects in addition to highly complex/nested third-party objects whose keys you cannot manipulate/convert for whatever reason, like a project time constraint).
E.g.:
h = {
:youtube => {
:search => 'daffy', # nested symbol key
'history' => ['goofy', 'mickey'] # nested string key
}
}
Method 1: JSON.parse - symbolizes all keys recursively => Does not preserve original mix
JSON.parse( h.to_json, {:symbolize_names => true} )
=> { :youtube => { :search=> "daffy", :history => ["goofy", "mickey"] } }
Method 2: ActiveSupport::JSON.decode - symbolizes top-level keys only => Does not preserve original mix
ActiveSupport::JSON.decode( ActiveSupport::JSON.encode(h) ).symbolize_keys
=> { :youtube => { "search" => "daffy", "history" => ["goofy", "mickey"] } }
Method 3: Marshal.load - preserves original string/symbol mix in the nested keys. PERFECT!
Marshal.load( Marshal.dump(h) )
=> { :youtube => { :search => "daffy", "history" => ["goofy", "mickey"] } }
Unless there is a drawback that I'm unaware of, I'd think Method 3 is the way to go.
Cheers
There isn't anything built in to do the trick, but it's not too hard to write the code to do it using the JSON gem. There is a symbolize_keys method built into Rails if you're using that, but that doesn't symbolize keys recursively like you need.
require 'json'
def json_to_sym_hash(json)
json.gsub!('\'', '"')
parsed = JSON.parse(json)
symbolize_keys(parsed)
end
def symbolize_keys(hash)
hash.inject({}){|new_hash, key_value|
key, value = key_value
value = symbolize_keys(value) if value.is_a?(Hash)
new_hash[key.to_sym] = value
new_hash
}
end
As Leventix said, the JSON gem only handles double quoted strings (which is technically correct - JSON should be formatted with double quotes). This bit of code will clean that up before trying to parse it.
Recursive method:
require 'json'
def JSON.parse(source, opts = {})
r = JSON.parser.new(source, opts).parse
r = keys_to_symbol(r) if opts[:symbolize_names]
return r
end
def keys_to_symbol(h)
new_hash = {}
h.each do |k,v|
if v.class == String || v.class == Fixnum || v.class == Float
new_hash[k.to_sym] = v
elsif v.class == Hash
new_hash[k.to_sym] = keys_to_symbol(v)
elsif v.class == Array
new_hash[k.to_sym] = keys_to_symbol_array(v)
else
raise ArgumentError, "Type not supported: #{v.class}"
end
end
return new_hash
end
def keys_to_symbol_array(array)
new_array = []
array.each do |i|
if i.class == Hash
new_array << keys_to_symbol(i)
elsif i.class == Array
new_array << keys_to_symbol_array(i)
else
new_array << i
end
end
return new_array
end
Of course, there is a json gem, but that handles only double quotes.
Another way to handle this is to use YAML serialization/deserialization, which also preserves the format of the key:
YAML.load({test: {'test' => { ':test' => 5}}}.to_yaml)
=> {:test=>{"test"=>{":test"=>5}}}
Benefit of this approach it seems like a format that is better suited for REST services...
The most convenient way is by using the nice_hash gem: https://github.com/MarioRuiz/nice_hash
require 'nice_hash'
my_str = "{ 'user': { 'name': 'foo', 'age': 40, 'location': { 'city' : 'bar', 'state': 'ca' } } }"
# on my_hash will have the json as a hash
my_hash = my_str.json
# or you can filter and get what you want
vals = my_str.json(:age, :city)
# even you can access the keys like this:
puts my_hash._user._location._city
puts my_hash.user.location.city
puts my_hash[:user][:location][:city]
If you think you might need both string and symbol keys:
JSON.parse(json_string).with_indifferent_access