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qpython to select columns from table
This is about qpython code. Let’s say we have a table named “t” with 2 columns “name” and “iq” in kdb:
from qpython import qconnection, qcollection q = qconnection.QConnection(host='localhost', port=5000): q.open() q("t:flip `name`iq!(`Dent`Beeblebrox`Prefect;98 42 126)")How can we pass the column name and table name through qpython? Thanks.
pseudo code:
q({select x from y}, "iq", "t") -
3 Replies
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Some ways:
q("{((),x)#y}", numpy.string_("iq"), numpy.string_("t")) q("{value"select ",string[x],"from ",string y}", "iq", "t") q("select %s from %s" % ("iq","t")) q("{?[y;();0b;{x!x}(),x]}", numpy.string_("iq"), numpy.string_("t"))- Using # https://code.kx.com/q/ref/take/
- Using value https://code.kx.com/q/ref/value/
- Python string formatting
- Functional select https://code.kx.com/q/basics/funsql/
Functional selects are the most powerful way https://code.kx.com/q/wp/parse-trees/
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Thanks @rocuinneagain. I was trying the functional select and have to convert the strings to <class ‘numpy.bytes_’> first (I am using python 3), i.e.
q("{?[y;();0b;{x!x}(),x]}", np.bytes_("iq"), np.bytes_("t")) -
See docs for more on how the library handles difference between symbols and strings:
https://qpython.readthedocs.io/en/latest/type-conversion.html#string-and-symbols
(Answer above updated to use
numpy.string_to pass symbols as needed)
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