如何使用Map对象查找数组的元素计数

Question

我有一段单词，想找到每个单词的计数，特别是使用 JavaScript 的

Map

对象。

我知道这可以使用

.get()

和

.set()

方法来实现，但我不确定如何实现。

下面是我的代码。

let paragraph = `Lorem ipsum donec nisi taciti et elit congue turpis, lobortis 
                 massa suscipit massa est a praesent metus egestas, conubia turpis 
                 in cursus libero pharetra praesent.
                 Per bibendum taciti sit taciti facilisis a bibendum nisl massa non 
                 aliquam sem auctor ipsum eros, massa sed cubilia porta primis 
                 felis elementum non fringilla conubia neque aenean urna.`

// Split the paragraph into an array of individual words.

let words = paragraph.match(/\w+/gi);

let map = new Map();

for (let i = 0; i < words.length; i++) {
  let word = words[i];
  map.set(word, 0);
  // Logic - if (map contains word) {
  // map.set(word, count += 1);
  // } else {
  // map.set(word, 1);
  // }
}

console.log(map);

Answer 1

将 Array#reduce 与 Map 一起使用。

对于每次迭代，在地图中设置单词。

a.get("Lorem")

将返回一个数字或未定义。

||

处理未定义的情况。然后添加 1。

Map#set 也返回地图对象。

const paragraph = `Lorem ipsum donec nisi taciti et elit congue turpis, lobortis massa suscipit massa est a praesent metus egestas, conubia turpis in cursus libero pharetra praesent.
Per bibendum taciti sit taciti facilisis a bibendum nisl massa non aliquam sem auctor ipsum eros, massa sed cubilia porta primis felis elementum non fringilla conubia neque aenean urna.`

const words = paragraph.match(/\w+/gi);

const res = words.reduce((a,c)=>{
  return a.set(c, (a.get(c)||0) + 1);
}, new Map());

console.log([...res]);

Answer 2

使用

Map

数据结构，您可以编写代码：

const paragraph = "Lorem ipsum donec nisi taciti et elit congue turpis, lobortis massa suscipit massa est a praesent metus egestas, conubia turpis in cursus libero pharetra praesent. Per bibendum taciti sit taciti facilisis a bibendum nisl massa non aliquam sem auctor ipsum eros, massa sed cubilia porta primis felis elementum non fringilla conubia neque aenean urna."

// Split the paragraph into an array of individual words.

let words = paragraph.match(/\w+/gi);

let map = new Map();

for (let i = 0; i < words.length; i++) {
    let word = words[i];
    // Here you check if map already got the word.
    if (map.has(word)) {
        map.set(word, map.get(word) + 1)
    } else {
        map.set(word, 0);
    }
}

console.log(map);

Answer 3

检查Map是否有key，如果有的话获取它并加1，否则就添加它。

let paragraph = `Lorem ipsum donec nisi taciti et elit congue turpis, lobortis massa suscipit massa est a praesent metus egestas, conubia turpis in cursus libero pharetra praesent.
Per bibendum taciti sit taciti facilisis a bibendum nisl massa non aliquam sem auctor ipsum eros, massa sed cubilia porta primis felis elementum non fringilla conubia neque aenean urna.`

// Split the paragraph into an array of individual words.

let words = paragraph.match(/\w+/gi);

let map = new Map();

for (let i = 0; i < words.length; i++) {
    let word = words[i];
    // Logic - if (map contains word) {
    if(map.get(word)){
        map.set(word, map.get(word) + 1);
    } else {
        map.set(word, 1);
    }
}

console.log(map);

Answer 4

检查 Map 是否已经有该键，然后将

1

添加到特定位置，如果没有，则将新的键值添加到 Map 中。

let paragraph = `Lorem ipsum donec nisi taciti et elit congue turpis, lobortis massa suscipit massa est a praesent metus egestas, conubia turpis in cursus libero pharetra praesent.
Per bibendum taciti sit taciti facilisis a bibendum nisl massa non aliquam sem auctor ipsum eros, massa sed cubilia porta primis felis elementum non fringilla conubia neque aenean urna.`


let words = paragraph.match(/\w+/gi);

let map = new Map();

for (let i = 0; i < words.length; i++) {
  let word = words[i];
  if(map.get(word)) {
    map.set(word, map.get(word)+1);
  } else {
    map.set(word, 1);
  }
}

console.log(...map);

Answer 5

在地图中设置值

paragraph.split(" ").forEach((word) => {
    yourMap.set(word, word.length);
});

从地图中提取值

Array.from(myMap.keys()).forEach((key, value) => {
    console.log(`Count of word ${key} is: ${value}`);
});