如何在字符串中找到2个最常见的字母并使用javascript返回一个新字符串

Question

I'm working on a problem that ask to take a string string and return a new string with the 2 most frequent letters in the string in alternating order.

my code:

var word = "pponoomababaaa";
var len = word.length;

function twoLetters (word){
var arr = []
word = word.split("")
for (var i = 0; i < word.length; i++){
    if ((arr[word[i]])) arr[word[i]] += 1
    else arr[word[i]] = 1
  }
return arr  // [ p: 2, o: 3, n: 1, m: 1, a: 5, b: 2 ]
}
twoLetters(word)

This returned arr has a length of 0, which I don't understand, so I can't really do anything with it. I have tried putting it into an object but it still has the same issue. How do get arr to equal a key:value pair and then find the 2 highest values and them add the keys to a string in alternating order. Am I going in the right direction with the code I have?

Answer 1

It works if you change your array to an object:

var word = "pponoomababaaa";
var len = word.length;

function twoLetters (word){
  var arr = {}
  word = word.split("")
  for (var i = 0; i < word.length; i++){
    if ((arr[word[i]])) arr[word[i]] += 1
    else arr[word[i]] = 1
  }
  return arr  // { p: 2, o: 3, n: 1, m: 1, a: 5, b: 2 }
}

twoLetters(word)

In JavaScript, arrays ( [] ) don't contain key-value pairs (well, sort of: the indexes are keys so-to-speak). The data structure you're looking for is a plain object ( {} ), which can hold key-value pairs.

Edit

Just to add a bit of clarification, you can add members onto an array ( [] ), but your array length will be 0. Here's the output from my browser console in Chrome, where you can see that you can add members onto the array itself. However this approach isn't recommended.

Answer 2

You can use Map for this

 var myMap = new Map(); var word = "pponoomababaaa"; var chars = word.split(""); chars.forEach(function(char) { if (!myMap.get(char)) { myMap.set(char, 1); } else { var count=myMap.get(char); count+=1; myMap.set(char,count); } }); for (var [key, value] of myMap.entries()) { console.log(key + " = " + value); } //if to copy to new array var newarr=Array.from(myMap); console.log(newarr); 

Hope this helps

Answer 3

var word = "pponoomababaaa";
var len = word.length;

function twoLetters (word){
var arr = []
word = word.split("")
for (var i = 0; i < word.length; i++){
    if ((arr[word[i]])) arr[word[i]] += 1
    else arr[word[i]] = 1
  }
console.log(arr.p)
return arr  // [ p: 2, o: 3, n: 1, m: 1, a: 5, b: 2 ]

}
twoLetters(word)

You're not creating an array, you're creating an object. It does have a key:value pair, as you'll see in the console.log(arr.p) For it to be an array, you would need to push into arr.

Answer 4

Here is your updated code with arr as an object( {} ) not an array( [] )

 var word = "pponoomababaaa"; var len = word.length; function twoLetters (word){ var arr = {}; word = word.split("") for (var i = 0; i < word.length; i++){ if ((arr[word[i]])) arr[word[i]] += 1 else arr[word[i]] = 1 } return arr; // [ p: 2, o: 3, n: 1, m: 1, a: 5, b: 2 ] } console.log(twoLetters(word)) 

Setting keys in array would turn it into an object. Your arr = [] was working fine in jsbin( http://jsbin.com/povimehiyu/)(check the console). But not here in code snippet, hence modified arr = {}

• Adding key-value in object won't create/update the length property.
• In your code above, adding key in arr changed it into an object, and length property was not updated whenever who were setting a key-value in your arr