lpd.js

#!/usr/bin/env node

const ignorecase = true;
const include = "abcdefghijklmnopqrstuvwxyz";

function lpd(data) {
  // prepare
  let distribution = {};
  let sum = 0;
  include.split('').forEach(c => distribution[c] = 0);

  // ignore case
  if (ignorecase) {
    data = data.toLowerCase();
  }

  // count
  data.split('').forEach(c => {
    if (include.indexOf(c) >= 0) {
      distribution[c]++;
      sum++;
    }
  });

  // calculate and round percentage
  include.split('').forEach(c => distribution[c] = Math.round(distribution[c] * 10000 / sum) / 100);

  return distribution;
}

// use stdin and stout when called directly
if (require.main === module) {
  let data = "";
  process.openStdin().on('data', (chunk) => data += chunk).on('end', () => console.log(JSON.stringify(lpd(data), null, 2)));
} else {
  // otherwise export as module
  exports = lpd;
}