Select only first rows in each h2o dataframe group_by group (for merging)? - h2o

Question

Is there a way to select only first rows in each h2o dataframe group_by group?
The reason for doing this is to merge some columns in an h2o dataframe into a group_by'ed version of that dataframe that was created to get some stats. based on particular groupings in the original.
Example, suppose had two dataframes like
df1
receipt_key b c item_id
------------------------
a1 1 2 1
a2 3 4 1
and
df2
receipt_key e f item_id
--------------------------
a1 5 6 1
a1 7 8 2
a2 9 10 1
would like to join them such that end up with dataframe
df3
receipt_key b c e f item_id
-----------------------------
a1 1 2 5 6 1
a2 3 4 9 10 1
Have tried doing something like df2.group_by('receipt_key').max('item_id') to merge into df1, but doing so only leaves the item_id column in the group's get_frame() dataframe (and even listing all of the columns in df2 to max() on would not give the right values as well as be cumbersome for my actual use case which has much more columns in df2).
Any ideas on how this could be done? Would simply deleting duplicates be sufficient to get the desired dataframe (though there appears to be barriers to doing this in h2o, see https://0xdata.atlassian.net/browse/PUBDEV-3292)?

Answer 1

here you go:
import h2o
h2o.init()
df1 = h2o.H2OFrame({'receipt_key': ['a1', 'a2'] , 'b':[1,3] , 'c':[2,4], 'item_id': [1,1]})
df1['receipt_key'] = df1['receipt_key'] .asfactor()
df2 = h2o.H2OFrame({'receipt_key': ['a1', 'a1','a2'] , 'e':[5,7,9] , 'f':[6,8,10], 'item_id': [1,2,1]})
df2['receipt_key'] = df2['receipt_key'].asfactor()
df3 = df1.merge(df2)
df_subset = df3[['receipt_key','b','c','e','f','item_id']]
print(df_subset)
receipt_key b c e f item_id
a1 1 2 5 6 1
a2 3 4 9 10 1