如何使用Lambda Expression获得单词平均长度 [英] How to get words average length using Lambda Expression

问题描述

我有一个单词列表文本文件，我想从该文件中获取最小，最大和平均单词长度。

I have a word list text file, I want to get min, max and average word lengths from that file.

我有一个流方法：

public static Stream<String> readWords(String filename) {
    try {
        BufferedReader reader = new BufferedReader(new FileReader(filename));
        Stream<String> stringStream = reader.lines();
        return stringStream;
    } catch (IOException exn) {
        return Stream.<String>empty();
    }
}

在我的主要测试方法中，我打印最大值和min

In my main method for testing I'm printing max and min

System.out.println(readWords(filename)
        .min(Comparator.comparing(s -> s.length()))
        .get()
        .length()
);
System.out.println(readWords(filename)
        .max(Comparator.comparing(s -> s.length()))
        .get()
        .length()
);

它按预期工作。

问题：

是否有可能像我在min和max中那样获得字长的平均值？在是或否的情况下，如何做到（仅作为Lambda表达式）？

Questions:
Is it possible to get the average of the word length like I did in min and max? In both case yes or no, how to do that (only as Lambda Expression)?

推荐答案

lines（）方法将为您提供一行而不是单词。获得 Stream 后，请致电 flatMap 用字替换行，提供lambda表达式拆分单词：

The lines() method will get you a stream of the lines, not the words. Once you have the Stream, call flatMap to replace the lines with the words, supplying the lambda expression to split out the words:

Stream<String> stringStream = reader.lines().flatMap( line -> 
    Stream.of(line.split("\\s+"))
);

这将纠正 max 的实施， 分钟。它还会影响您希望实现的任何平均计算的正确性。

This will correct your implementation of max and min. It also affects the correctness of any average calculation you wish to implement.

要获得平均值，您可以调用 mapToInt 将单词流映射到它们的长度（产生 IntStream ），然后调用 平均 ，其中返回 OptionalDouble 。

To obtain the average, you can call mapToInt to map the stream of words to their lengths (yielding an IntStream), then call average, which returns an OptionalDouble.

System.out.println(readWords(filename)
    .mapToInt( s -> s.length() )  // or .mapToInt(String::length)
    .average()
    .getAsDouble());

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