Merging of two dictionaries

This question already has an answer here:

How to merge two dictionaries in a single expression? 48 answers

---

I want to merge these two dictionaries and the result should be as follows:

D3={'a':1,'b':2,'c':3,'b':2,'c':3,'d':1}

how can I achieve this in python?

You can't. You can only have one value per key in a Python dict. What you can do is to have a list or a set as the value.

Here is an example with a set:

d1 = { 'a': 1, 'b': 2, 'c': 3 }
d2 = { 'a': 1, 'b': 5, 'd': 4 }
d3 = {}
def add_dict(target, d):
    for key in d:
        target.setdefault(key, set([])).add(d[key])

add_dict(d3, d1)
add_dict(d3, d2)

This will give you d3 :

{'a': set([1]), 'c': set([3]), 'b': set([2, 5]), 'd': set([4])}

You can also do this with a list (possibly closer to your example):

d1 = { 'a':1, 'b':2, 'c': 3}
d2 = { 'b':2 ,'c':3, 'd': 1}
d3 = {}
def add_dict(target, d):
    for key in d:
        target.setdefault(key, []).append(d[key])

add_dict(d3, d1)
add_dict(d3, d2)

You'll get this:

{'a': [1], 'c': [3, 3], 'b': [2, 2], 'd': [1]}

However, looking at {'a':1,'b':2,'c':3,'b':2,'c':3,'d':1} (which can't be a dict), it seems that you're after a different data structure altogether. Perhaps something like this:

d1 = { 'a':1, 'b':2, 'c': 3}
d2 = { 'b':2 ,'c':3, 'd': 1}
result = []

result += [ { 'key': key, 'value': d1[key] } for key in d1 ]
result += [ { 'key': key, 'value': d2[key] } for key in d2 ]

This would produce this, which looks closer to the data structure you had in mind initially:

[ {'value': 1, 'key': 'a'},
  {'value': 3, 'key': 'c'},
  {'value': 2, 'key': 'b'},
  {'value': 3, 'key': 'c'},
  {'value': 2, 'key': 'b'},
  {'value': 1, 'key': 'd'} ]

---

You may want to try:

D3 = {}
D3.update(D1)
D3.update(D2)

Here, we're creating an empty dictionary D3 first, then update it from the two other dictionaries.

Note that you need to be careful with the order of the updates: if D2 shares some keys with D1 , the code above will overwrite the corresponding entries of D1 with those of D2 .

Note as well that the keys will not be repeated. The example you give D3={a:1,b:2,c:3,b:2,c:3,d:1} is not a valid dictionary.

---

Dictionaries by definition can't have duplicate keys, so "merging" dictionaries will actually give the following result (note the order is arbitrary):

{'a': 1, 'b': 2, 'c': 3, 'd': 1}

You can create a clone of one of the dictionaries and merge the entries from the other into it:

D3 = dict(D1)
D3.update(D2)

or you can create a new dictionary from the concatenation of the (key, value) tuples from each input dictionary:

D3 = dict(D1.items() + D2.items())

If you really want multiple values for duplicate keys, you need something like a list of values for each key:

from itertools import groupby
dict(( (key, [v for k, v in group]) for key, group in groupby(sorted(D1.items() + D2.items()), lambda x: x[0])))

链接地址: http://www.djcxy.com/p/17564.html

上一篇: python：通过相同的键值合并字典

下一篇: 合并两本字典