如何转换数组？

Question

I have the following task:

Your task is to implement the function transform(arr) that takes an array and returns transformed array, based on the control sequences that arr contains. Control sequences are defined string elements of the mentioned array:

• --discard-next excludes the next element of the array from the transformed array.
• --discard-prev excludes the previous element of the array from the transformed array.
• --double-next doubles the next element of the array in the transformed array.
• --double-prev doubles the previous element of the array in the transformed array.

For example:

transform([1, 2, 3, '--double-next', 4, 5]) => [1, 2, 3, 4, 4, 5]

transform([1, 2, 3, '--discard-prev', 4, 5]) => [1, 2, 4, 5]

The function must not affect initial array. Control sequences are applied from left to right. Control sequences do not fall into the transformed array. Control sequences in initial array don't occur in a row. If there is no element next to the control sequence to which it can be applied, it does nothing. The function should throw an Error if the arr is not an Array .

I've written the following code:

 let transform = function (arr) { for (let i = 0; i < arr.length; i++) { if (arr[i] === '--discard-next') { let result = arr.slice(0, i) + "," + arr.slice(i + 2); let newArray = result.split(','); return newArray; } else if (arr[i] === '--discard-prev') { let result = arr.slice(0, i - 1) + "," + arr.slice(i + 1); let newArray = result.split(','); return newArray; } else if (arr[i] === '--double-next') { let result = arr.slice(0, i) + "," + arr[i + 1] + "," + arr.slice(i + 1); let newArray = result.split(','); return newArray; } else if (arr[i] === '--double-prev') { let result = arr.slice(0, i) + "," + arr[i - 1] + "," + arr.slice(i + 1); let newArray = result.split(','); return newArray; } } }; console.log(transform([1, 2, 3, '--double-next', 4, 5])); // => [1, 2, 3, 4, 4, 5] console.log(transform([1, 2, 3, '--discard-prev', 4, 5])); // => [1, 2, 4, 5]

What's wrong with it?

Answer 1

You could flatMap the values and have a look ahead or behind of the wanted transformation.

 let transform = array => array.flatMap((v, i, a) => { if (a[i + 1] === '--discard-prev') return []; if (a[i - 1] === '--double-next') return [v, v]; if (a[i + 1] === '--double-prev') return [v, v]; if (v.toString().startsWith('--d')) return []; return v; }); console.log(...transform([1, 2, 3, '--double-next', 4, 5])); // [1, 2, 3, 4, 4, 5] console.log(...transform([1, 2, 3, '--discard-prev', 4, 5])); // [1, 2, 4, 5] console.log(...transform([1, 2, 3, '--double-prev', 4, 5])); // [1, 2, 3, 3, 4, 5]

Answer 2

Use .join(','); that will remove the new line or remove .split(',') .

 let transform = function (arr) { for (let i = 0; i < arr.length; i++) { if (arr[i] === '--discard-next') { let result = arr.slice(0, i) + "," + arr.slice(i + 2); let newArray = result; return newArray; } else if (arr[i] === '--discard-prev') { let result = arr.slice(0, i - 1) + "," + arr.slice(i + 1); let newArray = result; return newArray; } else if (arr[i] === '--double-next') { let result = arr.slice(0, i) + "," + arr[i + 1] + "," + arr.slice(i + 1); let newArray = result; return newArray; } else if (arr[i] === '--double-prev') { let result = arr.slice(0, i) + "," + arr[i - 1] + "," + arr.slice(i + 1); let newArray = result; return newArray; } } }; console.log('[',transform([1, 2, 3, '--double-next', 4, 5]),']'); // => [1, 2, 3, 4, 4, 5] console.log('[',transform([1, 2, 3, '--discard-prev', 4, 5]),']'); // => [1, 2, 4, 5]