Returns the maximum value in a designated column of a Google Spreadsheet

getMax.gs

/**
 * Returns the maximum value in a designated column
 * @param {sheet} sheet Target sheet
 * @param {number} numCol Column number of target column
 * @param {number} initialValue Initial value
 * @return {number} max The largest number in target column
*/
function getMax(sheet, numCol, initialValue) {
  initialValue = initialValue || 0;
  var data = sheet.getRange(2, numCol, sheet.getLastRow()-1).getValues(); // First row of sheet used as header row
  var max = data.reduce(function(accu, cur){return Math.max(accu, cur)}, initialValue);
  return max;
}