Making a dictionary for value in a dictionary in Python

Question

I am trying to add dictionaries which have a key from each element from the list and value(s) from one following element from the list and a count for the number of times it follows it, in dictionary format. For example, if we have the list of words, ['The', 'cat', 'chased', 'the', 'dog'] and if the key is "the", I want the values to be {‘dog’: 1, ‘cat’: 1}. The entire output should be {‘the’: {‘dog’: 1, ‘cat’: 1}, ‘chased’: {‘the’: 1}, ‘cat’: {‘chased’: 1}}.

My code so far can generate key and values but not in dictionary in dictionary format. Could someone help on this?

My code:

line = ['The', 'cat', 'chased', 'the', 'dog']
output = {}
for i, item in enumerate(line):
    print(i, item, len(line))
    if i != len(line) - 1:
        output[item] = line[i+1]=i
print(output)

Output:

{'The': 'cat', 'chased': 'the', 'the': 'dog', 'cat': 'chased'}

Answer 1

I did not test it but something like that maybe? Using defaultdict:

from collections import defaultdict

line = ['The', 'cat', 'chased', 'the', 'dog']
output = defaultdict(lambda: defaultdict(int))

for t, token in enumerate(line[:-1]):
    output[token.lower()][line[t + 1].lower()] += 1

Answer 2

You can use collections.Counter for this. Example -

line = ['The', 'cat', 'chased', 'the', 'dog','the','dog']
from collections import Counter
output = {}
for i, item in enumerate(line):
    print(i, item, len(line))
    if i != len(line) - 1:
        output.setdefault(item.lower(),Counter()).update(Counter({line[i+1]:1}))

print(output)

.setdefault() first checks if the key exists, if it doesn't it sets it to the second argument and then returns the value at that key.

In Counter , when you do .update() , if the key already exists, it increases the count by 1 , so this seems like the correct structure to use for your case.

Also, Counter behave just like normal dictionary, so you can later on use them just as any dictionary.

---

Demo (Please do note the modified input to show a scenario where 'dog' followed 'the' twice) -

>>> line = ['The', 'cat', 'chased', 'the', 'dog','the','dog']
>>> from collections import Counter
>>> output = {}
>>> for i, item in enumerate(line):
...     print(i, item, len(line))
...     if i != len(line) - 1:
...         output.setdefault(item.lower(),Counter()).update(Counter({line[i+1]:1}))
...
0 The 7
1 cat 7
2 chased 7
3 the 7
4 dog 7
5 the 7
6 dog 7
>>> print(output)
{'dog': Counter({'the': 1}), 'cat': Counter({'chased': 1}), 'chased': Counter({'the': 1}), 'the': Counter({'dog': 2, 'cat': 1})}