Convert a number to an alphabet letter

Question

What I want is a function that takes in input a number and returns an alphabet letter (a-z).

This is my code (I get it from this question):

function numberToLetter(value) {
  const roundedPositiveValue = Math.round(Math.abs(value))
  return (roundedPositiveValue + 9).toString(36)
  // return ((roundedPositiveValue % 26) + 9).toString(36)
}

function print(value) {
  document.write(`${value} → ${numberToLetter(value)}<br>`)
}

[-10, -2, 0, 2.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 200].forEach(v => print(v))

It works but not in every case. For example it doesn't work for values > 26, so I tried using the modulo operator but in that case (commented line), it doesn't work for value 26. How can I fix it?

what results do you want from negative values or values greater than 26, or values with decimal places? — Nina Scholz, Mar 16 '21 at 08:40
@NinaScholz _"negative values"_ -> `Math.abs(value)`, _"decimal places"_ -> `Math.round(...)` — Andreas, Mar 16 '21 at 08:44

score 3 · Accepted Answer · answered Mar 16 '21 at 08:46

3

You could subtract one, to get a zero based value, apply modulo and add one to get values from one to 26.

function numberToLetter(value) {
    const adjusted = ((Math.round(Math.abs(value)) - 1) % 26) + 1;
    return (adjusted + 9).toString(36);
}

function print(value) {
    document.write(`${value} → ${numberToLetter(value)}<br>`)
}

[-10, -2, 0, 2.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 200].forEach(v => print(v))

answered Mar 16 '21 at 08:46

Nina Scholz

376,160
25
347
392

Thanks, it works. Why -1 inside `adjusted`? – whitecircle Mar 16 '21 at 09:18
because you need a zero based value. any value with rest operator returns a value from 0 to a value smaller than the second operand. later you need a value starting with one. – Nina Scholz Mar 16 '21 at 09:21

Convert a number to an alphabet letter

1 Answers1