| freq_table | tabulate simple frequencies |
| is_id | Make sure the match type is correct |
| merge | Merge two tables |
| possible_ids | Find possible unique identifies of data frame |
| x1 | Testing data x1 |
| x2 | Testing data x2 |
| x3 | Testing data x3 |
| x4 | Testing data x4 |
| y1 | Testing data y1 |
| y2 | Testing data y2 |
| y3 | Testing data y3 |
| y4 | Testing data y4 |