code: public static Writable min(JavaRDD<List<Writable>> allData, String columnName, Schema schema){
          int columnIdx = schema.getIndexOfColumn(columnName);
          JavaRDD<Writable> col = allData.map(new SelectColumnFunction(columnIdx));
          return col.min(Comparators.forType(schema.getType(columnName).getWritableType()));
      }
docs: Get the minimum value for the specified column
  
  @param allData    All data
  @param columnName Name of the column to get the minimum value for
  @param schema     Schema of the data
  @return           Minimum value for the column