Question

我试图在java Stream中实现map-reduce范例这个1命令。例如，我有各种客户的订单列表，每个订单都有订单状态，客户ID和订单金额：

<style>    
.address{
    position: absolute;
    left: 234px;
    bottom: 160px;
    width: 110px;
    height: 115px;
}
</style>

<script>   
$('.address').click(function(){
for(var i=0;i<=$('.address').length;i++){
            switch (i) {            
                case 0 :
                 $('.embed-container, .maps').html('<iframe src="https://www.google.com/maps/embed?pb=!1m18!1m12!1m3!1d945.7084267048235!2d73.8854388291583!3d18.536415399212462!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x0%3A0xdda3387f821de029!2sWink+%26+Nod!5e0!3m2!1sen!2sin!4v1525613363322" width="100%" height="400" frameborder="0" scrolling="no" marginheight="0" marginwidth="0"></iframe>'); 
                break;
                case 1 : 
                $('.embed-container, .maps').html('<iframe src="https://www.google.com/maps/embed?pb=!1m18!1m12!1m3!1d3784.450403270009!2d73.81459871445705!3d18.463246687442403!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x3bc2956a20fbac17%3A0x91987f7033fd2e3c!2sAbhiruchi+Mall+and+Multiplex!5e0!3m2!1sen!2sin!4v1525612885113" width="100%" height="400" frameborder="0" scrolling="no" marginheight="0" marginwidth="0"></iframe>'); 
                break;    
                default:
                $('.embed-container, .maps').html(' <iframe src="https://www.google.com/maps/embed?pb=!1m18!1m12!1m3!1d945.7084267048235!2d73.8854388291583!3d18.536415399212462!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x0%3A0xdda3387f821de029!2sWink+%26+Nod!5e0!3m2!1sen!2sin!4v1525613363322" width="100%" height="400" frameborder="0" scrolling="no" marginheight="0" marginwidth="0"></iframe>'); 
                break;     
            }
        }
  });
</script>

我想得到每个客户的金额总和。

做这样的事情，并不是由客户对总和进行分组，而是计算所有客户的总和：

import React, { Component } from "react";
import { render } from "react-dom";

class CView extends Component {
  someFunc() {
    alert(1);
  }

  render() {
    return <div>Hello, there</div>;
  }
}

class App extends Component {
  getControl() {
    this.cv = <CView />;
    return this.cv;
  }

  render() {
    return (
      <div>
        <h2 onClick={() => this.cv.someFunc()}>Click Me</h2>
        {this.getControl()}
      </div>
    );
  }
}

render(<App />, document.getElementById("root"));

有人有任何想法吗？

Answer 1

为了为每个Customer生成单独的总计，您需要按客户ID对Customer进行分组（使用collect(Collectors.groupingBy())）。然后，您可以使用Collectors.summingInt()对每组Customer的数量进行求和：

Map<String,Integer> totals = 
    customers.stream()
    .filter(a->a.status.equals("A"))
    .collect(Collectors.groupingBy(Customer::getID,
                                   Collectors.summingInt(Customer::getAmount)));

这将返回以下Map：

{cust1=750, cust2=1568, cust3=845, cust4=86}

使用java流实现map-reduce

1 个答案: