Question

I need to store objects that have a number (>2) of integer member variables and do quick look-ups using any member variables as a search key.

For easier illustration let’s say the objects are tuples of 3 integers and I need to do quick look-ups using any element of a tuple as a key in a list of such tuples:

collection = [(1, 200, 9), 
              (2, 300, 8), 
              (3, 400, 7)]

Look-ups would be like:

collection.lookup_by_first_element(1) # Return (1, 200, 9)
collection.lookup_by_second_element(300) # Return (2, 300, 8)
collection.lookup_by_third_element(250) # Return None

I need the lookups to be fast/efficient. My best bet so far is to use an in memory sqlite database with three columns for the three tuple elements and put indexes on all three columns.

A search tree would also do, but those have one key for lookup and I don’t see how could I do lookups based on more than one key. How would you do it?

Answer 1

Using numpy:

>>> import numpy as np
>>> collection = [(1, 200, 9),
...               (2, 300, 8),
...               (3, 400, 7)]
>>> collection = np.array(collection)
>>> def f(d, c, v):
...     # d: collection, c: column, v: value
...     if np.any(d[:, c]==v): return d[d[:, c]==v]
...     return 'None'
...
>>> f(collection, 0, 1)
array([[  1, 200,   9]])
>>> f(collection, 1, 300)
array([[  2, 300,   8]])
>>> f(collection, 2, 250)
'None'