Question

目前我有一个定义为var myArray = [(Date, Double)]()的元组数组。

myArray的输出可能如下所示：

[(2016-08-30 07:00:00 +0000, 1.0), (2016-09-30 07:00:00 +0000, 0.050000000000000003), 
(2016-10-30 07:00:00 +0000, 20.0), (2017-06-30 07:00:00 +0000, 6.0), 
(2017-07-30 07:00:00 +0000, 5.0)]

我正在尝试从元组数组中获取最大Double值，但不知道如何去做。

我看到有一个功能：

myArray.max { (<#(Date, Double)#>, <#(Date, Double)#>) -> Bool in 

}

但是，如果使用正确的功能，我还不确定如何使用它？

有人能指出我正确的方向吗？

Answer 1

max与sort类似。您必须通过比较$0 < $1。结果是具有最大值的（可选）元组。

if let maxItem = myArray.max(by: {$0.1 < $1.1 }) {
    let maxDouble = maxItem.1
}

再一次，不鼓励您使用元组作为数据源

来自documentation：

如果您的数据结构可能会超出临时范围，请将其建模为类或结构，而不是作为元组。

Answer 2

您可以使用以下解决方案

[TestClass]
public class DiscardWhileBusyActionBlockTest
{
    [TestMethod]
    public void PostToConnectedBuffer_ActionNotBusy_MessageConsumed()
    {
        var actionPerformer = new ActionPerformer();

        var block = new DiscardWhileBusyActionBlock<int>(actionPerformer.Perform);
        var buffer = DiscardWhileBusyActionBlockTest.SetupBuffer(block);

        buffer.Post(1);

        DiscardWhileBusyActionBlockTest.WaitForCompletion(buffer, block);

        var expectedMessages = new[] { 1 };
        actionPerformer.LastReceivedMessage.Should().BeEquivalentTo(expectedMessages);
    }

    [TestMethod]
    public void PostToConnectedBuffer_ActionBusy_MessagesConsumedWhenActionBecomesAvailable()
    {
        var actionPerformer = new ActionPerformer();

        var block = new DiscardWhileBusyActionBlock<int>(actionPerformer.Perform);
        var buffer = DiscardWhileBusyActionBlockTest.SetupBuffer(block);

        actionPerformer.SetBusy();

        // 1st message will set the actionperformer to busy, 2nd message should be sent when
        // it becomes available.
        buffer.Post(1);
        buffer.Post(2);

        actionPerformer.SetAvailable();

        DiscardWhileBusyActionBlockTest.WaitForCompletion(buffer, block);

        var expectedMessages = new[] { 1, 2 };
        actionPerformer.LastReceivedMessage.Should().BeEquivalentTo(expectedMessages);
    }

    [TestMethod]
    public void PostToConnectedBuffer_ActionBusy_DiscardMessagesInBetweenAndProcessOnlyLastMessage()
    {
        var actionPerformer = new ActionPerformer();

        var block = new DiscardWhileBusyActionBlock<int>(actionPerformer.Perform);
        var buffer = DiscardWhileBusyActionBlockTest.SetupBuffer(block);

        actionPerformer.SetBusy();

        buffer.Post(1);
        buffer.Post(2);
        buffer.Post(3);
        buffer.Post(4);
        buffer.Post(5);

        actionPerformer.SetAvailable();

        DiscardWhileBusyActionBlockTest.WaitForCompletion(buffer, block);

        var expectedMessages = new[] { 1, 5 };
        actionPerformer.LastReceivedMessage.Should().BeEquivalentTo(expectedMessages);
    }

    private static void WaitForCompletion(IDataflowBlock source, IDataflowBlock target)
    {
        source.Complete();
        target.Completion.Wait(TimeSpan.FromSeconds(1));
    }

    private static BufferBlock<int> SetupBuffer(ITargetBlock<int> block)
    {
        var buffer = new BufferBlock<int>();
        buffer.LinkTo(block);
        buffer.Completion.ContinueWith(task => block.Complete());
        return buffer;
    }

    private class ActionPerformer
    {
        private readonly ManualResetEvent resetEvent = new ManualResetEvent(true);

        public List<int> LastReceivedMessage { get; } = new List<int>();

        public void Perform(int message)
        {
            this.resetEvent.WaitOne(TimeSpan.FromSeconds(3));
            this.LastReceivedMessage.Add(message);
        }

        public void SetBusy()
        {
            this.resetEvent.Reset();
        }

        public void SetAvailable()
        {
            this.resetEvent.Set();
        }
    }
}

或者使用$ syntax

let max = myArray.max { (left, right) -> Bool in
    return left.1 < right.1
}

Answer 3

试试这个：

myArray.max { (val1, val2) -> Bool in
    return val1.1 < val2.1
}

Answer 4

此代码给出了给定数组的最大值

var myArray = [(2016-08-30, 1.0), (2016-09-30, 0.050000000000000003),
 (2016-10-30, 20.0), (2017-06-30, 6.0),
 (2017-07-30, 5.0)]
// Get maximum element

var max = myArray.max {
    $0.1 < $1.1
}

print(max!.1)

Answer 5

为max添加一个闭包。

let maxTuple = myArray.max{ $0.1 < $1.1 }!
let maxDouble = maxTuple.1

如何在Swift中获取元组数组的最大Double值？

5 个答案: