How do I compare two hashes?
RubyHashRuby Problem Overview
I am trying to compare two Ruby Hashes using the following code:
#!/usr/bin/env ruby
require "yaml"
require "active_support"
file1 = YAML::load(File.open('./en_20110207.yml'))
file2 = YAML::load(File.open('./locales/en.yml'))
arr = []
file1.select { |k,v|
file2.select { |k2, v2|
arr << "#{v2}" if "#{v}" != "#{v2}"
}
}
puts arr
The output to the screen is the full file from file2. I know for a fact that the files are different, but the script doesn't seem to pick it up.
Ruby Solutions
Solution 1 - Ruby
You can compare hashes directly for equality:
hash1 = {'a' => 1, 'b' => 2}
hash2 = {'a' => 1, 'b' => 2}
hash3 = {'a' => 1, 'b' => 2, 'c' => 3}
hash1 == hash2 # => true
hash1 == hash3 # => false
hash1.to_a == hash2.to_a # => true
hash1.to_a == hash3.to_a # => false
You can convert the hashes to arrays, then get their difference:
hash3.to_a - hash1.to_a # => [["c", 3]]
if (hash3.size > hash1.size)
difference = hash3.to_a - hash1.to_a
else
difference = hash1.to_a - hash3.to_a
end
Hash[*difference.flatten] # => {"c"=>3}
Simplifying further:
Assigning difference via a ternary structure:
difference = (hash3.size > hash1.size) \
? hash3.to_a - hash1.to_a \
: hash1.to_a - hash3.to_a
=> [["c", 3]]
Hash[*difference.flatten]
=> {"c"=>3}
Doing it all in one operation and getting rid of the difference variable:
Hash[*(
(hash3.size > hash1.size) \
? hash3.to_a - hash1.to_a \
: hash1.to_a - hash3.to_a
).flatten]
=> {"c"=>3}
Solution 2 - Ruby
You can try the hashdiff gem, which allows deep comparison of hashes and arrays in the hash.
The following is an example:
a = {a:{x:2, y:3, z:4}, b:{x:3, z:45}}
b = {a:{y:3}, b:{y:3, z:30}}
diff = HashDiff.diff(a, b)
diff.should == [['-', 'a.x', 2], ['-', 'a.z', 4], ['-', 'b.x', 3], ['~', 'b.z', 45, 30], ['+', 'b.y', 3]]
Solution 3 - Ruby
If you want to get what is the difference between two hashes, you can do this:
h1 = {:a => 20, :b => 10, :c => 44}
h2 = {:a => 2, :b => 10, :c => "44"}
result = {}
h1.each {|k, v| result[k] = h2[k] if h2[k] != v }
p result #=> {:a => 2, :c => "44"}
Solution 4 - Ruby
Solution 5 - Ruby
You could use a simple array intersection, this way you can know what differs in each hash.
hash1 = { a: 1 , b: 2 }
hash2 = { a: 2 , b: 2 }
overlapping_elements = hash1.to_a & hash2.to_a
exclusive_elements_from_hash1 = hash1.to_a - overlapping_elements
exclusive_elements_from_hash2 = hash2.to_a - overlapping_elements
Solution 6 - Ruby
I developed this to compare if two hashes are equal
def hash_equal?(hash1, hash2)
array1 = hash1.to_a
array2 = hash2.to_a
(array1 - array2 | array2 - array1) == []
end
The usage:
> hash_equal?({a: 4}, {a: 4})
=> true
> hash_equal?({a: 4}, {b: 4})
=> false
> hash_equal?({a: {b: 3}}, {a: {b: 3}})
=> true
> hash_equal?({a: {b: 3}}, {a: {b: 4}})
=> false
> hash_equal?({a: {b: {c: {d: {e: {f: {g: {h: 1}}}}}}}}, {a: {b: {c: {d: {e: {f: {g: {h: 1}}}}}}}})
=> true
> hash_equal?({a: {b: {c: {d: {e: {f: {g: {marino: 1}}}}}}}}, {a: {b: {c: {d: {e: {f: {g: {h: 2}}}}}}}})
=> false
Solution 7 - Ruby
If you need a quick and dirty diff between hashes which correctly supports nil in values you can use something like
def diff(one, other)
(one.keys + other.keys).uniq.inject({}) do |memo, key|
unless one.key?(key) && other.key?(key) && one[key] == other[key]
memo[key] = [one.key?(key) ? one[key] : :_no_key, other.key?(key) ? other[key] : :_no_key]
end
memo
end
end
Solution 8 - Ruby
If you want a nicely formatted diff, you can do this:
# Gemfile
gem 'awesome_print' # or gem install awesome_print
And in your code:
require 'ap'
def my_diff(a, b)
as = a.ai(plain: true).split("\n").map(&:strip)
bs = b.ai(plain: true).split("\n").map(&:strip)
((as - bs) + (bs - as)).join("\n")
end
puts my_diff({foo: :bar, nested: {val1: 1, val2: 2}, end: :v},
{foo: :bar, n2: {nested: {val1: 1, val2: 3}}, end: :v})
The idea is to use awesome print to format, and diff the output. The diff won't be exact, but it is useful for debugging purposes.
Solution 9 - Ruby
... and now in module form to be applied to a variety of collection classes (Hash among them). It's not a deep inspection, but it's simple.
# Enable "diffing" and two-way transformations between collection objects
module Diffable
# Calculates the changes required to transform self to the given collection.
# @param b [Enumerable] The other collection object
# @return [Array] The Diff: A two-element change set representing items to exclude and items to include
def diff( b )
a, b = to_a, b.to_a
[a - b, b - a]
end
# Consume return value of Diffable#diff to produce a collection equal to the one used to produce the given diff.
# @param to_drop [Enumerable] items to exclude from the target collection
# @param to_add [Enumerable] items to include in the target collection
# @return [Array] New transformed collection equal to the one used to create the given change set
def apply_diff( to_drop, to_add )
to_a - to_drop + to_add
end
end
if __FILE__ == $0
# Demo: Hashes with overlapping keys and somewhat random values.
Hash.send :include, Diffable
rng = Random.new
a = (:a..:q).to_a.reduce(Hash[]){|h,k| h.merge! Hash[k, rng.rand(2)] }
b = (:i..:z).to_a.reduce(Hash[]){|h,k| h.merge! Hash[k, rng.rand(2)] }
raise unless a == Hash[ b.apply_diff(*b.diff(a)) ] # change b to a
raise unless b == Hash[ a.apply_diff(*a.diff(b)) ] # change a to b
raise unless a == Hash[ a.apply_diff(*a.diff(a)) ] # change a to a
raise unless b == Hash[ b.apply_diff(*b.diff(b)) ] # change b to b
end
Solution 10 - Ruby
Here is algorithm to deeply compare two Hashes, which also will compare nested Arrays:
HashDiff.new(
{val: 1, nested: [{a:1}, {b: [1, 2]}] },
{val: 2, nested: [{a:1}, {b: [1]}] }
).report
# Output:
val:
- 1
+ 2
nested > 1 > b > 1:
- 2
Implementation:
class HashDiff
attr_reader :left, :right
def initialize(left, right, config = {}, path = nil)
@left = left
@right = right
@config = config
@path = path
@conformity = 0
end
def conformity
find_differences
@conformity
end
def report
@config[:report] = true
find_differences
end
def find_differences
if hash?(left) && hash?(right)
compare_hashes_keys
elsif left.is_a?(Array) && right.is_a?(Array)
compare_arrays
else
report_diff
end
end
def compare_hashes_keys
combined_keys.each do |key|
l = value_with_default(left, key)
r = value_with_default(right, key)
if l == r
@conformity += 100
else
compare_sub_items l, r, key
end
end
end
private
def compare_sub_items(l, r, key)
diff = self.class.new(l, r, @config, path(key))
@conformity += diff.conformity
end
def report_diff
return unless @config[:report]
puts "#{@path}:"
puts "- #{left}" unless left == NO_VALUE
puts "+ #{right}" unless right == NO_VALUE
end
def combined_keys
(left.keys + right.keys).uniq
end
def hash?(value)
value.is_a?(Hash)
end
def compare_arrays
l, r = left.clone, right.clone
l.each_with_index do |l_item, l_index|
max_item_index = nil
max_conformity = 0
r.each_with_index do |r_item, i|
if l_item == r_item
@conformity += 1
r[i] = TAKEN
break
end
diff = self.class.new(l_item, r_item, {})
c = diff.conformity
if c > max_conformity
max_conformity = c
max_item_index = i
end
end or next
if max_item_index
key = l_index == max_item_index ? l_index : "#{l_index}/#{max_item_index}"
compare_sub_items l_item, r[max_item_index], key
r[max_item_index] = TAKEN
else
compare_sub_items l_item, NO_VALUE, l_index
end
end
r.each_with_index do |item, index|
compare_sub_items NO_VALUE, item, index unless item == TAKEN
end
end
def path(key)
p = "#{@path} > " if @path
"#{p}#{key}"
end
def value_with_default(obj, key)
obj.fetch(key, NO_VALUE)
end
module NO_VALUE; end
module TAKEN; end
end
Solution 11 - Ruby
This was answered in "Comparing ruby hashes". Rails adds a diff method to hashes. It works well.
Solution 12 - Ruby
what about convert both hash to_json and compare as string? but keeping in mind that
require "json"
h1 = {a: 20}
h2 = {a: "20"}
h1.to_json==h1.to_json
=> true
h1.to_json==h2.to_json
=> false
Solution 13 - Ruby
How about another, simpler approach:
require 'fileutils'
FileUtils.cmp(file1, file2)