Array of hashes to hash
RubyArraysHashRuby Problem Overview
For example, I have array of single hashes
a = [{a: :b}, {c: :d}]
What is best way to convert it into this?
{a: :b, c: :d}
Ruby Solutions
Solution 1 - Ruby
You may use
a.reduce Hash.new, :merge
which directly yields
{:a=>:b, :c=>:d}
Note that in case of collisions the order is important. Latter hashes override previous mappings, see e.g.:
[{a: :b}, {c: :d}, {e: :f, a: :g}].reduce Hash.new, :merge # {:a=>:g, :c=>:d, :e=>:f}
Solution 2 - Ruby
You can use .inject
:
a.inject(:merge)
#=> {:a=>:b, :c=>:d}
Which initiates a new hash on each iteration from the two merged. To avoid this, you can use destructive :merge!
( or :update
, which is the same):
a.inject(:merge!)
#=> {:a=>:b, :c=>:d}
Solution 3 - Ruby
These two are equivalent:
total_hash = hs.reduce({}) { |acc_hash, hash| acc_hash.merge(hash) }
total_hash = hs.reduce({}, :merge)
Note that Hash#merge
creates a new hash on each iteration, which may be a problem if you are building a big one. In that case, use update
instead:
total_hash = hs.reduce({}, :update)
You can also convert the hashes to pairs and then build the final hash:
total_hash = hs.flat_map(&:to_a).to_h
Solution 4 - Ruby
I came across this answer and I wanted to compare the two options in terms of performance to see which one is better:
a.reduce Hash.new, :merge
a.inject(:merge)
using the ruby benchmark module, it turns out that option (2) a.inject(:merge)
is faster.
code used for comparison:
require 'benchmark'
input = [{b: "c"}, {e: "f"}, {h: "i"}, {k: "l"}]
n = 50_000
Benchmark.bm do |benchmark|
benchmark.report("reduce") do
n.times do
input.reduce Hash.new, :merge
end
end
benchmark.report("inject") do
n.times do
input.inject(:merge)
end
end
end
the results were
user system total real
reduce 0.125098 0.003690 0.128788 ( 0.129617)
inject 0.078262 0.001439 0.079701 ( 0.080383)
Solution 5 - Ruby
Just use
a.reduce(:merge)
#=> {:a=>:b, :c=>:d}
Solution 6 - Ruby
Try this
a.inject({}){|acc, hash| acc.merge(hash)} #=> {:a=>:b, :c=>:d}
Solution 7 - Ruby
You can transform it to array [[:a, :b]]
and after that translate everything to hash {:a=>:b}
# it works like [[:a, :b]].to_h => {:a=>:b}
[{a: :b}, {c: :d}].map { |hash| hash.to_a.flatten }.to_h
# => {:a=>:b, :c=>:d}