code: function meanSummarizer(column, tableData, columns) {
    var stats = tableData.reduce(function (stats, rowData, rowNumber) {
      var sortValue = Utils.getSortValue(column, rowData, rowNumber, tableData, columns);
  
      if (sortValue) {
        if (stats.sum === null) {
          stats.sum = sortValue;
        } else {
          stats.sum += sortValue;
        }
      }
  
      return stats;
    }, { sum: null, count: tableData.length, mean: null });
  
    if (stats.sum !== null) {
      stats.mean = stats.sum / stats.count;
    }
  
    return stats;
  }
docs: Computes the mean, sum, and count in a column as `mean, sum, count`.
  Does the computation based on the sortValue.
  
  @param {Object} column The column definition
  @param {Object[]} tableData the data for the whole table
  @param {Object[]} columns The definitions of columns for the whole table
  
  @return {Object} The mean of values as `{ mean, sum, count }`