使用array.reduce方法计算重复元素 [英] Using array.reduce method to count duplicate elements

问题描述

我正在编写一个关于函数JS的教程，我需要使用reduce方法的挑战：

I'm working through a tutorial on functional JS and I'm up to a challenge requiring the use of the reduce method:

给出一个随机数组的单词，输出一个数组，显示单词加上它的单词数，例如： ['apple，'orange，'grape'，'apple'] - > ['apple：2'，'orange：1'，'grape：1]

Given a random array of words, output an array that shows the word plus it's word count, for instance: ['apple, 'orange, 'grape', 'apple'] -> ['apple: 2','orange: 1', 'grape: 1]

我知道这不正确使用reduce，但这是我的半工作解决方案：

I know this isn't the correct use of reduce, but here was my semi-working solution:

var wordCountsArray = inputWords.map(function(item){
    var counter = 0;
    var itemCount = inputWords.reduce(function(prevVal, curVal){
        if(curVal==item){
            counter++;
        }
        return;
    },0);

    return item+": "+counter;
})

return wordCountsArray;  

}

这确实输出了字数，但字数列表有重复，即看起来像：

This did indeed output the word counts, but the word count list has duplicates, i.e. looks like:

['apple: 2','orange: 1', 'grape: 1, 'apple: 2']

而不是

['apple: 2','orange: 1', 'grape: 1]

我查了MSDN的方法指南，Mozilla的，几个博客。我得到它作为累加器如何工作，但因为它使用最后一次迭代的输出作为下一个的输入，我不知道如何将它应用于此任务。我不需要解决方案，但也许需要帮助理解？

I've looked up MSDN's guide on the method, Mozilla's, several blogs. I get how it works as an accumulator, but because it uses the output of the last iteration as input for the next, I have no idea how to apply it to this task. I don't need a solution, but maybe a little help in understanding?

推荐答案

我知道这是一个解决方案，但有时候解决方案是最好的解释。在第一个块中跟随fruitsCount对象。请注意，fruitsArray只是该对象的翻译，所以应该很容易理解。

I know this is a solution, but sometimes solutions are the best explanations. Follow the "fruitsCount" object in the first block. Note that "fruitsArray" is simply a translation of this object, so that should be very easy to understand.

var fruits = ['apple', 'orange', 'grape', 'apple'].reduce(function(fruitsCount, currentFruit){
    if(typeof fruitsCount[currentFruit] !== "undefined"){
      fruitsCount[currentFruit]++; 
      return fruitsCount;
    } else {
        fruitsCount[currentFruit]=1; 
        return fruitsCount;
    }
}, {});

var fruitsArray = [];
for(var x in fruits){
    fruitsArray.push(x + ": " + fruits[x]);
}

console.log(fruitsArray);

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