Modifying Values to Specific Keys in Python dictionary

Question

I have created a dictionary d below and am looking for a dictionary with the key ('a','b','c') to have values 'd' and 'e'.

test = ['a','b','c','d','a','b','c','e','p','q','r','s']
test2= tuple(test)
d = {test2[i:i+3]:test2[i+3] for i in range(0,len(test2)-3,1)}
print(d)

The output is:

{('a', 'b', 'c'): 'e', ('b', 'c', 'd'): 'a', ('c', 'd', 'a'): 'b', ('d', 'a', 'b'): 'c', ('b', 'c', 'e'): 'p', ('c', 'e', 'p'): 'q', ('e', 'p', 'q'): 'r', ('p', 'q', 'r'): 's'}

The intended output is:

{('a', 'b', 'c'): ('d','e'), ('b', 'c', 'd'): 'a', ('c', 'd', 'a'): 'b', ('d', 'a', 'b'): 'c', ('b', 'c', 'e'): 'p', ('c', 'e', 'p'): 'q', ('e', 'p', 'q'): 'r', ('p', 'q', 'r'): 's'}

Question: Looking at the first comment, the key takes its most recent value e and so now I'm trying to change the code to achieve the desired output? Thanks.

Answer 1

Option 1:

This create d using defaultdict (d = defaultdict(list)).

It loops through the data in a for loop. Multiple values are appended into a list

from collections import defaultdict

d = defaultdict(list)  # create list by default
for i in range(0,len(test2)-3):
  d[test2[i:i+3]].append(test2[i+3]) # append value into dictionary entry
                                     # which is a list 
                                     # since we used d = defaultdict(list)

Option 2: Similar in form to option 1, but uses normal dictionary with setdefault to have key entries be lists

d = {}
for i in range(0,len(test2)-3):
  d.setdefault(test2[i:i+3], []).append(test2[i+3])

Both Options Have the Same Output

defaultdict(<class 'list'>,
            {   ('a', 'b', 'c'): ['d', 'e'],
                ('b', 'c', 'd'): ['a'],
                ('b', 'c', 'e'): ['p'],
                ('c', 'd', 'a'): ['b'],
                ('c', 'e', 'p'): ['q'],
                ('d', 'a', 'b'): ['c'],
                ('e', 'p', 'q'): ['r'],
                ('p', 'q', 'r'): ['s']})

Answer 2

Heres a another solution you can try out as well:

from collections import defaultdict

test = ['a','b','c','d','a','b','c','e','p','q','r','s']

d = defaultdict(list)
while len(test) >= 4:
    *key, value = test[:4] # key -> a, b, c  value -> d
    d[tuple(key)].append(value)
    test = test[1:]

print(d)
# defaultdict(<class 'list'>, {('a', 'b', 'c'): ['d', 'e'], ('b', 'c', 'd'): ['a'], ('c', 'd', 'a'): ['b'], ('d', 'a', 'b'): ['c'], ('b', 'c', 'e'): ['p'], ('c', 'e', 'p'): ['q'], ('e', 'p', 'q'): ['r'], ('p', 'q', 'r'): ['s']})

The basic idea is that it keeps shrinking the list test until less than 4 items are left, and groups the first three items (a, b, c) into a tuple, then the last character d as a value.