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  • each-Select

    While Ruby’s each method is useful, it also comes with an awesome extended family of methods that are even more powerful!

    For the next few examples, we’ll work with a slightly more complex data structure. It look like this:

    friends = [
      {
        name: "Diego",
        status: "Online"
      },
      {
        name: "Liam",
        status: "Away"
      },
      {
        name: "Gloria",
        status: "Online"
      },
      {
        name: "Charlie",
        status: "Away"
      }
    ]

    select is similar to each in that we pass it a block to run on each element in the collection, but the similarities stop there. The important difference is that select will return a new collection with only the items that the block returned true for. It sounds pretty intimidating at first, so let’s walk through an example.

    We can use select to create a new Array filled with only our online friends:

    online_friends = friends.select do |friend|
      friend[:status] == "Online"
    end

    Because the block is so short, it would also work well as a one-liner:

    online_friends = friends.select{|friend| friend[:status] == "Online"}

    select will go through each element one at a time, starting with {name: “Diego”, status: “Online”}, passing it to the block we wrote. The block contains a single line: friend[:status] == “Online”. That line returns either true or false. If the block returns true, that specific item is added to a new Array that will be returned at the very end of select.

    This table shows each step of the process:

     
     

    At the very end, select returns this Array which we save to a new online_friends variable:

    [{ name: "Diego", status: "Online"}, { name: "Gloria", status: "Online"}]
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  • 原文地址:https://www.cnblogs.com/iwangzheng/p/5449010.html
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