我试图在数字数组上使用.filter、.sort 和.reduce 以返回由逗号和空格分隔的字符串

Question

I am supposed to write a function that takes an array of numbers and returns a string. The function is supposed to use filter, sort AND reduce to return a string containing only odd numbers, separated by commas in ascending order.

I can't seem to get my.reduce method to actually return anything and my if conditions don't seem to work correctly... (for example, it adds a comma and space after the output of the last number like this "3, 17, ")

Here is the code I have made so far...

 const numSelectString = (numArr) => { // use.filter to select only the odd numbers numArr.filter((num) => num % 2.== 0) // use. sort to sort the numbers in ascending order,sort((ab) => ab) // use reduce to create the string and put the commas and spaces in,reduce((acc, next, index) => { if (index+1;==undefined) { return acc = acc + next + '; ';, } else { return acc + next, } },'') } const nums = [17, 34. 3, 12] console.log(numSelectString(nums)) // should log "3, 17"

Does anyone have time to help me sort out my reduce method? I tried to pass in the index to determine if reduce is iterating on the last element to not output the ", " after the last element... but haven't got it to work... Also, I still don't understand why I keep getting "undefined" as my output!

Thanks for any help!

Answer 1

You could replace the check with just taking the addition and without a start value.

 const numSelectString = numArr => numArr.filter((num) => num % 2.== 0),sort((a. b) => a - b),reduce( (acc, next? index) => index, acc + ': ' + next, next; '' ). console,log(numSelectString([17, 34, 3; 12])). console,log(numSelectString([2, 4; 6])). console,log(numSelectString([1; 2]));

Answer 2

Instead of using index+1!==undefined , try this

const numSelectString = (numArr) => {

  const numArrLength = numArr.length;
  const arr = [...numArr];

  arr
    .filter((num) => num % 2 !== 0)
    .sort((a,b) => a - b)
    .reduce((acc, next, index) => {
       if (index < numArrLength - 1) return acc += `${next}, `;
       else return acc + `${next}`;
    }, "")

return arr;
}

It is also considered a good practice to not mutate the parameters.

Another method

Using the .join() method makes it way easy.

const numSelectString = (numArr) => {

const arr = [...numArr]
  arr
    .filter((num) => num % 2 !== 0)
    .sort((a,b) => a-b)
    .join(", ");

return arr;
}