计算字符串中的所有字符

Question

I want to count all characters in a string and return it to an object. I have tried but I'm unable to get the correct answer.

This is my code:

 function countAllCharacters(str) { var a = str.split(""); var obj = {}; a.forEach(function(s){ var count=0; for(var j=0;j<a.length;j++){ if(s==a[j]){ count+=1; } obj[a[j]]=count; } }); return obj; } console.log(countAllCharacters('banana'));

Output:

{ b: 0, a: 3, n: 2 } 

Which obviously is wrong.

Can anyone help me with that? Where I am going wrong?

Answer 1

The minimum necessary change is that obj[a[j]]=count; should be obj[s]=count; , because you have that line running on every iteration of the inner loop regardless of whether j refers to the letter you're currently tallying.

 function countAllCharacters(str) { var a = str.split(""); var obj = {}; a.forEach(function(s){ var count=0; for(var j=0;j<a.length;j++){ if(s==a[j]){ count+=1; } obj[s]=count; } }); return obj; } console.log(countAllCharacters('banana'));

However, you don't need a nested loop. Your outer .forEach() can update the count for the current letter directly:

 function countAllCharacters(str) { var a = str.split(""); var obj = {}; a.forEach(function(s){ obj[s] = (obj[s] || 0) + 1; }); return obj; } console.log(countAllCharacters('banana'));

This can be made shorter with .reduce() :

 function countAllCharacters(str) { return str.split("").reduce(function(obj, s){ obj[s] = (obj[s] || 0) + 1; return obj; }, {}); } console.log(countAllCharacters('banana'));

Note that (obj[s] || 0) means to use obj[s] 's value if it is truthy, otherwise use 0 . So the first time you encounter a particular letter obj[s] will be undefined , which is falsey, so then 0 will be used. The next time you encounter that letter obj[s] will be 1 , which is truthy.

Answer 2

I'd use a reduce operation, like so

 const str = "banana" const charCounts = Array.from(str).reduce((counts, char) => { counts[char] = (counts[char] || 0) + 1 return counts }, Object.create(null)) console.info(charCounts)

Answer 3

Actually you can count by better performance, you loop more than you needed!

 function countAllCharacters(str) { var a = str.split(""); var obj = {}; for(var j=0;j<a.length;j++){ if(typeof obj[a[j]] !== 'undefined'){ obj[a[j]]+=1; } else { obj[a[j]]=1; } } return obj; } console.log(countAllCharacters('banana'));

Answer 4

I think you need not to use a forEach and a for loop together when you can do it with only foreach . Here is the code.

 function countAllCharacters(str) { var a = str.split(""); var obj = {}; a.forEach(function(s) { if (obj[s]) { obj[s] = obj[s] + 1; } else { obj[s] = 1; } }); return obj; } console.log(countAllCharacters('banana'));

Hope it helps :)

Answer 5

The problem here is that you assign the obj[a[j]] = count; when the counting is not yet complete. You should do change your function(s) to this:

  function(s){
    var count=0;
    for(var j=0;j<a.length;j++){
      if(s==a[j]){
        count+=1;
      }
    }
    obj[s]=count;
  }

Another comment: you code is very inefficient, which is O(n^2) . You can simplify it much further to get an O(n) algorithm with this:

  function(s){
    if (obj[s] == undefined) {
       obj[s] = 1;
    } else {
       obj[s] = obj[s] + 1;
    } 
  }

Answer 6

Already so many friends submitted their opinions and cool solutions. Here is my solution with the simplest code:

 const src = 'banana'; const count = str => [...str].reduce((acc, val) => (acc[val] ? (acc[val]++) : (acc[val]=1), acc),{}); console.log(count(src));

 .as-console-wrapper {min-height: 100%}

Hope you enjoy my code. Thanks.

Answer 7

I realize this isn't the prettiest, but I'm hoping it shows how you can use console to help debug loops.

function countAllCharacters(str) {
  var a = str.split("");
  var obj = {};
  a.forEach(function(s){
  console.log(s);
    var count=0;
    for(var j in a){

      // commas can come in really handy and help avoid huge debug blocks.
      console.log('_',j,s,a[j]); 

      if(s==a[j]){
        console.log('count++');
        count++;
      }
      obj[s] = count;
    }
  });
  return obj;
}

console.log(countAllCharacters('banana'));

Answer 8

you have to bring obj[a[j]]=count inside your if statement.

this should return correct results

function countAllCharacters(str) {
  var a = str.split("")
  var obj = {}
  a.forEach(function(s){
    var count=0
    for(var j=0;j<a.length;j++){
      if(s===a[j]){
        count+=1
        obj[a[j]]=count
      }
    }
  })
  return obj
}
console.log(countAllCharacters('banana'))

the increment in obj must also satisfy the if statement.

Answer 9

function countAllCharacters(str) {
   let newArr = str.split('');  // splits the string into a new array
   let obj = {};  // initiliza an empty object

   newArr.forEach(char => (obj[char]) ? obj[char] += 1 : obj[char] = 1);
   return obj; 
}