Python将两个列表合并到字典中，添加值

Question

Given the two following lists, one containing strings, one integers, how can I merge these two lists into a dictionary while ADDING the values for duplicate keys?

stringlist = ["EL1", "EL2", "EL1", "EL3", "El4"]

integerlist = [1, 2, 12, 4, 5]

So in the final dictionary I'd like EL1 to be 13, because it also contains 1 and 12.

resultdictionary = {}
for key in appfinal:
    for value in amountfinal:
        resultdictionary[key] = value
        amountfinal.remove(value)
        break

In this case, result dictionary removes any duplicate keys, but takes the last value that matches those keys. So, EL1 would be 12.

Any ideas? Thank you.

Answer 1

Use defaultdict() to create a dictionary that automatically creates keys as needed.

Use zip() to loop over the two lists together.

from collections import defaultdict

resultdictionary = defaultdict(int)
for key, val in zip(stringlist, integerlist):
    resultdictionary[key] += val

Answer 2

One possible solution is to use dict.get with defaultvalue 0 . For example:

stringlist = ["EL1", "EL2", "EL1", "EL3", "El4"]
integerlist = [1, 2, 12, 4, 5]

resultdictionary = {}
for s, i in zip(stringlist, integerlist):
    resultdictionary[s] = resultdictionary.get(s, 0) + i

print(resultdictionary)

Prints:

{'EL1': 13, 'EL2': 2, 'EL3': 4, 'El4': 5}

Answer 3

Zany solution for funsies:

stringlist = ["EL1", "EL2", "EL1", "EL3", "El4"]

integerlist = [1, 2, 12, 4, 5]

result = {}
result.update((k, result.get(k, 0) + v) for k, v in zip(stringlist, integerlist))
print(result)

Try it online!

It's almost a one-liner, but still needs result to be defined as an empty dict first , so it can use a genexpr that lazily checks the value summed so far as it goes.

I don't actually recommend this. For one thing, I'm not sure the language spec strictly requires that dict.update evaluate the argument provided lazily; if it tried to optimize by eagerly converting it to a dict first, then merging, this would fail. For another, it's easily broken (a maintainer might blindly convert the genexpr to a dictcomp or listcomp and now it's eager and broken). And the genexpr, while it technically has no side-effects itself, is relying on the side-effects of it being consumed by result.update , which is a distinctly non-functional design at odds with the functional style of genexprs.

Answer 4

The quickest way w/o imports would be like this:

stringlist = ["EL1", "EL2", "EL1", "EL3", "El4"]

integerlist = [1, 2, 12, 4, 5]

#Convert two Lists into Dictionary using zip()
mergeLists = dict(zip(stringlist, integerlist))