code: public RecordList getUniqueRecordsBy(String fieldName) {
          Set<String> uniqueKeys = new HashSet<String>();
          final RecordListBuilder uniqueRecordListBuilder = new RecordListBuilder(schema);
          for (int rowIndex = 0; rowIndex < this.size(); rowIndex++) {
              final Record currentRecord = this.records.get(rowIndex);
              String uniqueKeyField = currentRecord.getValueByFieldName(fieldName);
              if(!uniqueKeys.contains(uniqueKeyField)){
                  uniqueRecordListBuilder.add(currentRecord);
              }
              uniqueKeys.add(uniqueKeyField);
          }
          return uniqueRecordListBuilder.createRecordList(dataSourceHash);
      }
docs: Picks the first available record by given fieldName
  @param fieldName the unique field value
  @return