来自两个列表的字典，包括键的多个值

Question

Is there a possibility to create a dict from two lists with same key occurring multiple times without iterating over the whole dataset?

Minimal example:

keys = [1, 2, 3, 2, 3, 4, 5, 1]
values = [1, 2, 3, 4, 5, 6, 7, 8]

# hoped for result:
dictionary = dict(???)
dictionary = {1 : [1,8], 2:[2,4], 3:[3,5], 4:[6], 5:[7]}

When using zip the key-value-pair is inserted overwriting the old one:

dictionary = dict(zip(keys,values))
dictionary = {1: 8, 2: 4, 3: 5, 4: 6, 5: 7}

I would be happy with a Multidict as well.

Answer 1

This is one approach that doesn't require 2 for loops

h = defaultdict(list)
for k, v in zip(keys, values):
    h[k].append(v)

print(h)
# defaultdict(<class 'list'>, {1: [1, 8], 2: [2, 4], 3: [3, 5], 4: [6], 5: [7]})

print(dict(h))
# {1: [1, 8], 2: [2, 4], 3: [3, 5], 4: [6], 5: [7]}

Answer 2

This is the only one-liner I could do.

dictionary = {k: [values[i] for i in [j for j, x in enumerate(keys) if x == k]] for k in set(keys)}

It is far from readable. Remember that clear code is always better than pseudo-clever code ;)

Answer 3

Here is an example that I think is easy to follow logically. Unfortunately it does not use zip like you would prefer, nor does it avoid iterating, because a task like this has to involve iterating In some form.

# Your data
keys = [1, 2, 3, 2, 3, 4, 5, 1]
values = [1, 2, 3, 4, 5, 6, 7, 8]

# Make result dict
result = {}
for x in range(1, max(keys)+1):
    result[x] = []

# Populate result dict
for index, num in enumerate(keys):
    result[num].append(values[index])

# Print result
print(result)

If you know the range of values in the keys array, you could make this faster by providing the results dictionary as a literal with integer keys and empty list values.