KDB+ query in QPython: Filter based on DataFrame list

Question

I am using qpython to query into a KDB+ database and then performing operations on the output. old_df is output from an earlier qpython sync query which has '[source_id]' as a string column. Now am querying into another database trades_database which has the same fields (as source_id) under a different column name customer (also string, no issues in data type)

params = np.array([])
for i in old_df['source_id']:
    params = np.append(params, np.string_(i))

new_df = q.sync('{[w]select from trade_database where customer in w}', *params, pandas=True)

Unfortunately, there is very little available online to solve such queries. I have learned a fair bit from the questions asked in here, but am really stuck here. My list could be very long and so would need to write a query where it is taken as an input only.

I also tried:

new_df= q1.sync('{select from trades_database where customer in (`1234, `ABCD)}', pandas=True)

which works but I get <qpython.qtype.QLambda object at 0x000000000413F710>

How does one "unpack" a QLambda object?

Please ignore the 2nd question if I am not allowed to ask 2 questions in the same post pls. Apologies in that case.

Thanks!

spiff · Accepted Answer · 2018-09-10 14:15:39Z

2

here is what I did and it seems to work:

    params = np.array(one_id) #just input the initial id used to search for old_df, and not put the square brackets to make it into a list

    for i in old_df['source_id']:
        params = np.append(params,np.string_(i))
    params=np.unique(params)

    new_df = q1.sync('{[w]select from trades_database where customer in w}', params, pandas=True)

answered Sep 10, 2018 at 14:15

spiff

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