Merge several Python dictionaries [duplicate]

You can iterate over the dictionaries directly — no need to use range. The setdefault method of dict looks up a key, and returns the value if found. If not found, it returns a default, and also assigns that default to the key.

super_dict = {}
for d in dicts:
    for k, v in d.iteritems():  # d.items() in Python 3+
        super_dict.setdefault(k, []).append(v)

Also, you might consider using a defaultdict. This just automates setdefault by calling a function to return a default value when a key isn’t found.

import collections
super_dict = collections.defaultdict(list)
for d in dicts:
    for k, v in d.iteritems():  # d.items() in Python 3+
        super_dict[k].append(v)

Also, as Sven Marnach astutely observed, you seem to want no duplication of values in your lists. In that case, set gets you what you want:

import collections
super_dict = collections.defaultdict(set)
for d in dicts:
    for k, v in d.iteritems():  # d.items() in Python 3+
        super_dict[k].add(v)

Related Contents:

  1. How do I merge two dictionaries in a single expression (take union of dictionaries)?
  2. How to merge dictionaries of dictionaries?
  3. How to merge multiple dicts with same key or different key?
  4. merging several python dictionaries
  5. Merging two CSV files using Python
  6. How do I merge two dictionaries in a single expression?
  7. merging Python dictionaries
  8. Merging dictionary value lists in python
  9. How to merge dicts, collecting values from matching keys?
  10. How do I merge two dictionaries in a single expression in Python?
  11. Pandas Merging 101
  12. Iterating over dictionaries using ‘for’ loops
  13. Get key by value in dictionary
  14. Split / Explode a column of dictionaries into separate columns with pandas
  15. Make a dictionary with duplicate keys in Python
  16. cartesian product in pandas
  17. How do I initialize a dictionary of empty lists in Python?
  18. Python list of dictionaries search
  19. Performant cartesian product (CROSS JOIN) with pandas
  20. Why can’t I use a list as a dict key in python?
  21. Remove duplicate dict in list in Python
  22. Modifying a Python dict while iterating over it
  23. Converting dictionary to JSON
  24. Python Dictionary Comprehension
  25. Access an arbitrary element in a dictionary in Python
  26. List of unique dictionaries
  27. Should I use ‘has_key()’ or ‘in’ on Python dicts?
  28. How to avoid “RuntimeError: dictionary changed size during iteration” error?
  29. Get the key corresponding to the minimum value within a dictionary
  30. How can I make a dictionary from separate lists of keys and values?
  31. How do you create nested dict in Python?
  32. How to sort objects by multiple keys?
  33. Hashing a dictionary?
  34. Thread Safety in Python’s dictionary
  35. Intersecting two dictionaries
  36. What do I do when I need a self referential dictionary?
  37. Comparing Python dictionaries and nested dictionaries
  38. How does the key argument in python’s sorted function work?
  39. How do I check that multiple keys are in a dict in a single pass?
  40. Remove dictionary from list
  41. Convert list into a dictionary [duplicate]
  42. Converting a list of tuples into a dict
  43. PySpark create new column with mapping from a dict
  44. Why does updating one dictionary object affect other? [duplicate]
  45. How to split dictionary into multiple dictionaries fast
  46. How do I extract all the values of a specific key from a list of dictionaries?
  47. Difference between defining typing.Dict and dict?
  48. Why do you have to call .items() when iterating over a dictionary in Python?
  49. How to generate all combination from values in dict of lists in Python
  50. Know the depth of a dictionary

Leave a Comment