如何在多行字符串中找到字符位置（行，列）？

Question

How i can find position of current character in multi-line string? If every line in a string was the same length it would be easy. Eg

const str = `hello
hello
hello`

const findPos = (str, ind) => {
  const [cols] = str.split('\n');
  return { row: ind / cols.length | 0, col: ind % cols.length };
};

findPos(str, 12) // { row: 2, col: 2 }

But how can i do it, if every row is different length? Eg

const str = `hello
from
my
old
friend!`

findPos(str , 12) // { row: 3, col: 1 }

Answer 1

Use a while loop to iterate over the split lines, subtracting the length of the current line from the number of characters to go. If the length is shorter than the number of characters to go, return the characters to go as the col , and the number of lines iterated over as the row :

 const findPos = (input, indexToFind) => { const lines = input.split('\n'); let charsToGo = indexToFind; let lineIndex = 0; while (lineIndex < lines.length) { const line = lines[lineIndex]; const char = line[charsToGo]; if (char) { return { row: lineIndex, col: charsToGo }; } charsToGo -= line.length; lineIndex++; } return 'None'; }; const str = `hello from my old friend!` console.log(findPos(str , 12)); // { row: 3, col: 1 }

Note that this does not consider the newlines as characters to be iterated over, which seems to be in line with your expected output. For an example of this generating a position for all characters in the string see the following snippet:

 const findPos = (input, indexToFind) => { const lines = input.split('\n'); let charsToGo = indexToFind; let lineIndex = 0; while (lineIndex < lines.length) { const line = lines[lineIndex]; const char = line[charsToGo]; if (char) { return { row: lineIndex, col: charsToGo }; } charsToGo -= line.length; lineIndex++; } return 'None'; }; const str = `hello from my old friend!` const lenWithoutNewlines = str.length - str.match(/\n/g).length; for (let i = 0; i < lenWithoutNewlines; i++) { console.log(findPos(str , i)); }

Answer 2

when your requirement is to find out the array of the location of each character

You don't need to create a function to find location one by one.

Also when creating the objects you can keep the placeholder and character for quick search.

 const str = `hello from my old friend!` function createPos(str) { let out = str.split('\n').map(e => [...e]); let place = 1; return out.map((arr, row) => arr.map((char, col) => ({ char, row, col, place: place++ }))).flat(); } function findPos(str, n) { return createPos(str).find(e => e.place === n) } console.log('all chars\n', createPos(str)); console.log('found char\n',findPos(str, 12))

Answer 3

My suggestion:

const findPosition = (input, indexToFind) => {
    const preChunk = input.substr(0, indexToFind);
    const row = preChunk.split('\n').length - 1;
    const lastIndexOfNewLine = input.lastIndexOf('\n', indexToFind);
    const col = lastIndexOfNewLine > 0 ? indexToFind - lastIndexOfNewLine - 1 : indexToFind;
    return {row, col};
};