为什么我的removeNumbersLessThan函数不能正常工作？

Question

I have to write a function that takes a number and an object and input and return an object that has removed all numbers less than the indicated number.

I completed a similar function on the previous problem in the problem set that did the opposite, removeNumbersGreaterThan. All I really did was copy that same code that worked on the previous problem and replaced the greater than symbol with a less than symbol, but for some reason it is not working in all cases.

I've already tried changing it to less than or equal to <= but that made no difference at all. Not sure what's going on!

 function removeNumbersLessThan(num, obj) { var i = 0; while (i < Object.keys(obj).length) { if (Object.values(obj)[i] < num) { delete obj[Object.keys(obj)[i]] } i++; } return obj; } //test var obj = { a: 4, b: 6, c: 5, d: 3 } removeNumbersLessThan(7, obj) console.log(obj) //returns b:6 d:3 -- should return empty object 

I noticed it returns the second value no matter what. Even if it is less than the num value. After adding some more elements to my object, I noticed that it skips over every other element in the object. I also found that the reason by previous opposite function worked was because the tests skipped over these cases. It also has the same issue, upon further investigation.

Answer 1

When your loop deletes a value from obj , that key will no longer be returned from Object.keys .
But you still increment the i counter, so you "skip" a key every time you delete a key from obj .

You can fix this by only getting the objects keys once and storing them before deleting properties:

 function removeNumbersLessThan(num, obj) { let keys = Object.keys(obj); for (let key of keys) { if (obj[key] < num) { delete obj[key]; } } return obj; } //test var obj = { a: 4, b: 6, c: 5, d: 3 }; removeNumbersLessThan(7, obj); console.log(obj); 

If you don't want to mutate the object, you could instead copy all properties that are greater than or equal to a new object:

 function removeNumbersLessThan(num, obj) { let result = {}; for(let [key, value] of Object.entries(obj)) if(value >= num) result[key] = value; return result; } let obj = { a: 4, b: 6, c: 5, d: 3, e: 8 }; console.log(removeNumbersLessThan(7, obj)); 

Answer 2

You mutate the object and get in every loop with a deleted property a new lenght in this vase the index is one ahead.

This solution is not advisable, because you get for every iteration new keys and values.

 function removeNumbersLessThan(num, obj) { var i = 0; while (i < Object.keys(obj).length) { if (Object.values(obj)[i] < num) { delete obj[Object.keys(obj)[i]]; } else { i++; // increment only if not deleted } } return obj; } var obj = { a: 4, b: 6, c: 5, d: 3 }; removeNumbersLessThan(7, obj); console.log(obj); // {} 

Instead you could get the keys with a for ... in statement . Then check with this key.

 function removeNumbersLessThan(num, object) { for (let key in object) { if (object[key] < num) { delete object[key]; } } return object; } var obj = { a: 4, b: 6, c: 5, d: 3 }; removeNumbersLessThan(7, obj); console.log(obj); // {} 

Answer 3

First, note that when you delete a key on the object (ie you mutate the object), the length property of the array returned by Object.keys() will decrease in every iteration, at the same time you increment the i variable on every iteration, so in the end you will not traverse all the properties of the object.

In this particular case, I will prefer using for ... in to traverse the objects keys instead of your while loop, using the next logic:

 function removeNumbersLessThan(num, obj) { for (const key in obj) { if (obj[key] < num) delete obj[key]; } return obj; } console.log(removeNumbersLessThan(7, {a:4, b:6, c:5, d:3})); console.log(removeNumbersLessThan(5, {a:4, b:6, c:5, d:3})); 

 .as-console {background-color:black !important; color:lime;} .as-console-wrapper {max-height:100% !important; top:0;} 

Answer 4

Using reduce version...

function removeNumbersLessThan(num, obj) {
  return Object.keys(obj).reduce((accum, next) => {       
        if (obj[next] >= num)
          return {...accum, [next]: obj[next]};
        else
          return accum;
  },{});
}

      //test
      var obj = {
        a:4,
        b:6,
        c:5,
        d:3
      } 

let x = removeNumbersLessThan(7,obj);

console.log(x);