Alphabet Array to Numeric Array

Puzzle

Write a function convert_alphabet_array which takes a contents array that contains alphabetical strings and returns an array of the numerical order of each element. This is useful for turning Excel-esque column labels into column numbers.

Examples

// INPUT
> var contents = ["C", "D", "A", "Z", "AA"];
> convert_alphabet_array(contents);

// OUTPUT
[3, 4, 1, 26, 27]; // A is the 1st letter, Z is the 26th letter, AA is the 27th letter etc.

Solution

How It Works

1. (Optional) Validate input parameters.
   • Ensure contents elements are alphabetical strings.
2. Create a letters helper string and an empty output array to return.
3. Loop through the contents array elements.
   • Loop through each element’s letters and calculate a running_total based on each letter’s position in our letters helper string.
     • Add the running_total to output.
4. Return output.

Code

/**
 *
 * Custom sorts an input array based on values in an indexes array.
 *
 * @param {array} contents - Input alphabetical array
 * @return {array} output - Numerical representation of input's order
 *
 **/
function convert_alphabet_array(contents) {

  // 1. (OPTIONAL) VALIDATION

  // Ensure contents is an array
  if (!Array.isArray(contents)) {
    throw new TypeError("contents parameter must be an array");
  }

  // Ensure contents elements are alphabetical strings
  if (contents.every(function(element) {

    if ((typeof element === "string") && (/^[a-zA-Z]+$/.test(element)) === true) {
      return true;
    };

  }) !== true) {

    throw new TypeError("contents array must contain alphabetical string elements");

  }

  // 2. OUTPUT ARRAY
  var output = [];

  var letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';


  // 3. MAIN LOOP

  // Loop through contents array elements
  for (var i = 0; i < contents.length; i++) {

    contents[i] = contents[i].toUpperCase();

    var running_total = 0;

    // Loop through the length of the current element
    for (var l = 0; l < contents[i].length; l++) {

      running_total += Math.pow(letters.length, l) * (letters.indexOf(contents[i].substr(((l + 1) * -1), 1)) + 1);

    };

    output.push(running_total);
  };

  return output;

};

References

• Stack Overflow - Convert excel column alphabet