从哈希数组中的每个组中获取第二项的聪明方法？

Question

The problem would be easy to solve with a manual loop and a result array, which you add onto as you go. But I'm looking for a more ruby-esque solution, probably something that uses inject or select. Here's the problem:

arr_of_hashes = [
  {id: 1, val: "blah1"},
  {id: 1, val: "blah2"},
  {id: 1, val: "blah3"},
  {id: 2, val: "blah4"},
  {id: 2, val: "blah5"},
  {id: 3, val: "blah6"},
  {id: 3, val: "blah7"},
  {id: 3, val: "blah8"},
  {id: 3, val: "blah9"}
]

"Groups" are defined by the "id" field in the hashes. We are guaranteed each group has at least two items. We want to return an array containing the 2nd item of each group:

output_should_be = [
  {id: 1, val: "blah2"},
  {id: 2, val: "blah5"},
  {id: 3, val: "blah7"}
]

Answer 1

"I'm looking for a more ruby-esque solution". I guess you mean functional :

arr_of_hashes.chunk { |h| h[:id] }.map { |id, hs| hs[1] }
#=> [{:id=>1, :val=>"blah2"}, {:id=>2, :val=>"blah5"}, {:id=>3, :val=>"blah7"}]

Use group_by if elements are not pre-ordered by id .

Answer 2

这是使用group_by的解决方案：

arr_of_hashes.group_by{|h| h[:id]}.to_a.map{|id,a| a[1]}