Find dictionary items whose key matches a substring

Question

I have a large dictionary constructed like so:

programs[\'New York\'] = \'some values...\' 
programs[\'Port Authority of New York\'] = \'some values...\' 
pr         


        

Answer 1

You could generate all substrings ahead of time, and map them to their respective keys.

#generates all substrings of s.
def genSubstrings(s):
    #yield all substrings that contain the first character of the string
    for i in range(1, len(s)+1):
        yield s[:i]
    #yield all substrings that don't contain the first character
    if len(s) > 1:
        for j in genSubstrings(s[1:]):
            yield j

keys = ["New York", "Port Authority of New York", "New York City"]
substrings = {}
for key in keys:
    for substring in genSubstrings(key):
        if substring not in substrings:
            substrings[substring] = []
        substrings[substring].append(key)

Then you can query substrings to get the keys that contain that substring:

>>>substrings["New York"]
['New York', 'Port Authority of New York', 'New York City']
>>> substrings["of New York"]
['Port Authority of New York']

Pros:

• getting keys by substring is as fast as accessing a dictionary.

Cons:

• Generating substrings incurs a one-time cost at the beginning of your program, taking time proportional to the number of keys in programs.
• substrings will grow approximately linearly with the number of keys in programs, increasing the memory usage of your script.
• genSubstrings has O(n^2) performance in relation to the size of your key. For example, "Port Authority of New York" generates 351 substrings.