Select Numpy Array of Objects by Objects Attributes

Question

I have a Numpy array of objects Equity, i.e.:

array([ Equity(24, symbol='AAPL', asset_name='APPLE INC', exchange='NASDAQ GLOBAL SELECT MARKET'),
   Equity(26578, symbol='GOOG_L', asset_name='GOOGLE INC', exchange='NASDAQ GLOBAL SELECT MARKET'),
   Equity(5061, symbol='MSFT', asset_name='MICROSOFT CORP', exchange='NASDAQ GLOBAL SELECT MARKET'),
   ...,
   Equity(20513, symbol='LOOK', asset_name='LOOKSMART LTD', exchange='NASDAQ CAPITAL MARKET', ),
   Equity(27133, symbol='WPCS', asset_name='WPCS INTERNATIONAL INC', exchange='NASDAQ CAPITAL MARKET'),
   Equity(27917, symbol='FREE', asset_name='FREESEAS INC', exchange='NASDAQ CAPITAL MARKET')], dtype=object)

The object Equity has the attribute exchange.

Which is the most concise method to get a subarray containing only Equity objects where exchange == 'NEW YORK STOCK EXCHANGE'?

Thanks!

When used like this a numpy array is basically the same as a Python list. There are few 'vectorized' operations that work on object elements. — hpaulj
– hpaulj, Commented Aug 5, 2015 at 18:27

yangjie · Accepted Answer · 2015-08-05 14:00:03Z

1

Suppose the numpy array is named equity_array.

Solution 1:

Use list comprehension

np.array([eqt for eqt in equity_array if eqt.exchange == 'NEW YORK STOCK EXCHANGE'])

Solution 2:

Use Python build-in function filter

np.array(filter(lambda x: x.exchange == 'NEW YORK STOCK EXCHANGE', equity_array))

Notice that in Python 3 filter returns a iterator so it should be

np.array(list(filter(lambda x: x.exchange == 'NEW YORK STOCK EXCHANGE', equity_array)))

edited Aug 5, 2015 at 14:00

answered Aug 5, 2015 at 12:45

yangjie

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