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
