将数组中的元素拆分为长度为 n 的字符串数组

Question

Each element in array have to be less than n characters in length, but as long as possible.

Elements from original array have to be joined by , (without space).

Let's say n is 20 .

I have this array:

[
  "first",
  "second",
  "third",
  "etc"
]

I want get this in a end:

[
  "first,second,third",
  "etc"
]

I tried using split and join .

array.split(2).join(',');

but splitting it in 2 is not smart, because array length can vary and I can't figure out better way, someone recommended me using reduce , but I can't understand reduce , still trying to learn it to use in real problems.

Answer 1

You might try something like this, using reduce:

const originalArray = [
  "first",
  "second",
  "third",
  "etc"
];

const maxSize = 20;

const reducer = (ac, val) => {
  if (ac.length > 0 && ac[ac.length - 1].length + val.length <= maxSize) {
    ac[ac.length - 1] += "," + val;
  } else {
    ac.push(val);
  }
  return ac;
};

const newArray = originalArray.reduce(reducer, []);

console.log(newArray);

What reduce does is, basically start with an empty array as a result. Then, process each single item of the original array in this way:

• If the sum of the lengths of the result array last item and the processing value is over the maxSize, or if the result array size is still empty, add it as a new result array item.
• Otherwise, add it as a separated with coma string to the current last item from the result array.

Answer 2

You can try this

const arr = ["first", "second", "third", "etc"];

const result = [];
let i = 0;
arr.forEach(word => {
    if (!result[i]) {
        result[i] = word;
    } else if (result[i].length + word.length + 1 <= 20) {
        result[i] += `,${word}`;
    } else {
        i += 1;
        result[i] = word;
    }
});
console.log(result); // prints ["first,second,third", "etc"]