Question

从以下哈希数组：

x = [
  {"creationDate"=>123456,"createdBy"=>"test_user1"},
  {"creationDate"=>123459,"createdBy"=>"test_user1"},
  {"creationDate"=>123458,"createdBy"=>"test_user1"},
  {"creationDate"=>123454,"createdBy"=>"test_user2"},
  {"creationDate"=>123452,"createdBy"=>"test_user2"},
  {"creationDate"=>123451,"createdBy"=>"test_user2"}
]

我正在尝试查找:creationDate值为:createdBy的最大"test_user1"值。我这样做了：

x.map {|a| a['creationDate'] if a['createdBy'] == 'test_user1'}
# => [123456,123459,123458,nil,nil,nil]

我想摆脱nil，以便我可以将max应用于该数组。如何修改上面的代码？

Answer 1

您想要做的是：

x.select { |record| record[:createdBy] == 'test_user1' }.map { |record| record[:creationDate] }.max
  # => 123459

一般情况下，要从数组中删除nil，您只需拨打Array#compact：

[1, nil, nil, 2, 'foo', nil].compact # => [1, 2, "foo"]

Answer 2

它接近你打算在python中做的事情：

x.select { |n| n[:createdBy] == "test_user1" }.max_by { |n| n[:creationDate] }

第一个操作选择“test_user1”创建的记录，而第二个操作根据creationDate获取结果数组的最大值

Answer 3

我猜是这样的：

x.delete_if {|x| x == nil}

Answer 4

这是地图缩减功能的理想选择，例如inject。

x = [{"creationDate" => 123456,"createdBy" => "test_user1"},
     {"creationDate" => 123459,"createdBy" => "test_user1"},
     {"creationDate" => 123458,"createdBy" => "test_user1"},
     {"creationDate" => 123454,"createdBy" => "test_user2"},
     {"creationDate" => 123452,"createdBy" => "test_user2"},
     {"creationDate" => 123451,"createdBy" => "test_user2"}]

x.inject(nil) do |result, item|
  if item["createdBy"] == "test_user1" && (result.nil? or item["creationDate"] > result)
    item["creationDate"]
  else
    result
  end
end

这是inject的可能实现。该块将迭代集合中的每个项目，并始终保持最高值。

Answer 5

isset()

 if(isset($_GET['ahosts']))

有条件地从哈希数组中提取哈希值

5 个答案: