Rails将哈希数组映射到单个哈希

Question

I have an array of hashes like so:

 [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]

And I'm trying to map this onto single hash like this:

{"testPARAM2"=>"testVAL2", "testPARAM1"=>"testVAL1"}

I have achieved it using

  par={}
  mitem["params"].each { |h| h.each {|k,v| par[k]=v} } 

But I was wondering if it's possible to do this in a more idiomatic way (preferably without using a local variable).

How can I do this?

Answer 1

You could compose Enumerable#reduce and Hash#merge to accomplish what you want.

input = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
input.reduce({}, :merge)
  is {"testPARAM2"=>"testVAL2", "testPARAM1"=>"testVAL1"}

Reducing an array sort of like sticking a method call between each element of it.

For example [1, 2, 3].reduce(0, :+) is like saying 0 + 1 + 2 + 3 and gives 6 .

In our case we do something similar, but with the merge function, which merges two hashes.

[{:a => 1}, {:b => 2}, {:c => 3}].reduce({}, :merge)
  is {}.merge({:a => 1}.merge({:b => 2}.merge({:c => 3})))
  is {:a => 1, :b => 2, :c => 3}

Answer 2

How about:

h = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
r = h.inject(:merge)

Answer 3

Use #inject

hashes = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
merged = hashes.inject({}) { |aggregate, hash| aggregate.merge hash }
merged # => {"testPARAM1"=>"testVAL1", "testPARAM2"=>"testVAL2"}

Answer 4

Here you can use either inject or reduce from Enumerable class as both of them are aliases of each other so there is no performance benefit to either.

 sample = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]

 result1 = sample.reduce(:merge)
 # {"testPARAM1"=>"testVAL1", "testPARAM2"=>"testVAL2"}

 result2 = sample.inject(:merge)
 # {"testPARAM1"=>"testVAL1", "testPARAM2"=>"testVAL2"}