merging python dictionaries with same keys

Question

I have a list of Python dictionaries with the same keys. I would like to create a big dictionary from the ones in the list. The thing is I cannot use update to create a new one because, as the keys are the same, the value for each key is overwritten in the process. A sample of my list is:

[{0: u'ChIJIxtmpVdCQg0R_TCH5ttvqC0',
  1: u'ChIJ2RMaMThvQg0R_6hmMXFiG_M',
  ...
  195: u'ChIJv1KfnmMpQg0R5iC9EmaXN6M',
  196: u'ChIJd0vQCiOEQQ0RasOKsxksdys'},
 {0: u'ChIJIxtmpVdCQg0R_TCH5ttvqC0',
  1: u'ChIJ2RMaMThvQg0R_6hmMXFiG_M',
  2: u'ChIJQ3PGOWlfQg0RkV-a6JQdrFs',
  3: u'ChIJ-TjccjhvQg0RVQmnPNgAJv4',
  ...
  100: u'ChIJN7zqEhgmQg0R-NzvqSYG_Ds',
  101: u'ChIJPTR-xaYoQg0RUrX7K8kQhU4',
  102: u'ChIJV_pHsIsoQg0ReGKLBXDqOc8',
  103: u'ChIJtXpyqps7Qg0RXq37551oP4o',...

What I want is a bigger dictionary of the following form:

{0: u'ChIJIxtmpVdCQg0R_TCH5ttvqC0',
  1: u'ChIJ2RMaMThvQg0R_6hmMXFiG_M',
  2: u'ChIJQ3PGOWlfQg0RkV-a6JQdrFs',
  3: u'ChIJ-TjccjhvQg0RVQmnPNgAJv4',
  ...
  195: u'ChIJv1KfnmMpQg0R5iC9EmaXN6M',
  196: u'ChIJd0vQCiOEQQ0RasOKsxksdys', ###HERE STARTS THE NEW DICT!!
  197: u'ChIJIxtmpVdCQg0R_TCH5ttvqC0',
  198: u'ChIJ2RMaMThvQg0R_6hmMXFiG_M',
  199: u'ChIJQ3PGOWlfQg0RkV-a6JQdrFs',
  ...

Where the keys increase up to the number of instances among all the dictionaries.

Thanks in advance.

What do you want to happen instead of overwriting the values of common keys? — steffen, Apr 12 '17 at 11:18
Dictionaries have no defined order. So how would the keys be numbered given the fact that iterating a dict doesn't produce a defined order of elements. — languitar, Apr 12 '17 at 11:19
@splinter Hi! so far I've only tried to update a blank dictionary with each dictionary of my list. The thing is that the values are overwritten, I would like to do like an "append" of dictionares, relabeling the keys, in fact the keys does not matter at all. — Gonzalo Donoso, Apr 12 '17 at 11:20
@steffen look the second box, at the end! I would like to create a new dict with all instances from the other dicts. — Gonzalo Donoso, Apr 12 '17 at 11:21
@languitar The list of dictionaries come from a enumerated loop. — Gonzalo Donoso, Apr 12 '17 at 11:22
Do you have to keep the order of each small dict in the big one? — Thierry Lathuille, Apr 12 '17 at 11:25
Is so much sample data really necessary? See how to create a [mcve]. — Peter Wood, Apr 12 '17 at 11:29
@steffen i don't know. Seems to be someone who doesn't like my question... — Gonzalo Donoso, Apr 13 '17 at 13:24

Burhan Khalid · Answer 1 · 2017-04-12T12:20:54.933

1

Try something like this:

vals = []
for d in list_of_dicts:
   vals.extend(d.values())

max_dict = dict(enumerate(vals))

edited Apr 12 '17 at 12:20

answered Apr 12 '17 at 11:22

Burhan Khalid

169,990
18
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You mean `vals.extend` – Thierry Lathuille Apr 12 '17 at 11:32
Once you correct the semantics (see ThierryLathuille 's comment), This runs as fast as my one-liner (see my answer), i.e. 20 faster than the accepted answer by yanneke . – steffen Apr 12 '17 at 12:17

yanneke · Accepted Answer · 2017-04-12T12:44:33.887

1

You could simply retreive the current size of the dictionary as key for each element.

myDict = {}
for dictionary in dictionaries:
  for key in dictionary:
    myDict[len(myDict)] = dictionary[key]

edited Apr 12 '17 at 12:44

answered Apr 12 '17 at 11:24

yanneke

106
7

3

`dict` is a Python builtin, you shouln't use it as a variable name. – Thierry Lathuille Apr 12 '17 at 11:36
1

This is slow. No offense, but my one-liner (see my answer) runs 20 times faster. – steffen Apr 12 '17 at 12:14

steffen · Answer 3 · 2017-04-12T12:36:24.130

0

If, as you say, the keys are sort of ids in the sense that they are consecutive integers, and you want to sort of append the values in the second dict, i.e. forget their original keys, then this could work:

dict(enumerate(list(dict1.values()) + list(dict2.values())))

If you have more than two source dictionaries, a little extra magic is necessary:

dict(enumerate([item for sublist in [list(d.values()) for d in dicts] for item in sublist]))

(The outer list comprehension is copied from the accepted answer to this question: Making a flat list out of list of lists in Python)

edited Apr 12 '17 at 12:36

answered Apr 12 '17 at 11:20

steffen

8,572
11
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90

The thing is I don't have only 2 dicts in my list, but 9. – Gonzalo Donoso Apr 12 '17 at 11:28
i didn't vote down! Thanks for your approach. Is very appreciate too! – Gonzalo Donoso Apr 13 '17 at 13:23

score 0 · Answer 4 · answered Apr 12 '17 at 11:29

0

To merge dict2 into dict1 this should work

dict1 = {1: 'a', 2: 'b'}
dict2 = {1: 'c', 2: 'd'}

max_key_in_dict1 = max(dict1.keys())
for key in dict2.keys():
    dict1[key+max_key_in_dict1] = dict2[key]
del dict2

dict1 is then:

{1: 'a', 2: 'b', 3: 'c', 4: 'd'}

answered Apr 12 '17 at 11:29

commoner

51
2

This is very slow. It runs roughly 80 times slower than my one-liner (see my answer) – steffen Apr 12 '17 at 12:22

merging python dictionaries with same keys

4 Answers4