Print all Unique Values in a Python Dictionary

Question

I'm struggling with a minor problem in Python (my program is in version 3.2.3 right now).

I have a dictionary that looks like this (this is just an example, actually taken from another post here):

[
    {"abc": "movies"},
    {"abc": "sports"},
    {"abc": "music"},
    {"xyz": "music"},
    {"pqr": "music"},
    {"pqr": "movies"},
    {"pqr": "sports"},
    {"pqr": "news"},
    {"pqr": "sports"},
]

I want to simply print() a list of unique values, eliminating duplicates. At the end of this list, I would like to print the number of unique values in the dictionary:

movies
sports
music
news

4

Any help is appreciated. There are some other posts here I found that were somewhat related, but I don't know Python well enough to apply it to this specific problem.

you have a *list* of dictionaries. – jfs Jun 20 '13 at 15:53 — jfs, Jun 20 '13 at 15:53

Ashwini Chaudhary · Answer 1 · 2015-08-27T08:31:51.397

62

Use set here as they only contain unique items.

>>> lis = [{"abc":"movies"}, {"abc": "sports"}, {"abc": "music"}, {"xyz": "music"}, {"pqr":"music"}, {"pqr":"movies"},{"pqr":"sports"}, {"pqr":"news"}, {"pqr":"sports"}]
>>> s = set( val for dic in lis for val in dic.values())
>>> s 
set(['movies', 'news', 'music', 'sports'])

Loop over this set to get the expected output:

for x in s:                                
    print x
print len(s)   #print the length of set after the for-loop
... 
movies
news
music
sports
4

This line s = set( val for dic in lis for val in dic.values()) is roughly equivalent to:

s = set()
for dic in lis:
   for val in dic.values():
      s.add(val)

edited Aug 27 '15 at 08:31

answered Jun 20 '13 at 15:48

Ashwini Chaudhary

244,495
58
464
504

6

Points for explaining the nested list comprehension. – Dawngerpony Nov 20 '13 at 21:38
3

That nested list is crazy, would have **never** thought of that. – Marshall Davis Aug 27 '15 at 03:48

Joe Silverstein · Answer 2 · 2019-05-13T07:46:44.740

30

You can exploit the properties of set for this purpose; each element is unique and duplicates will be ignored.

uniqueValues = set(myDict.values())

By using set in this way, duplicate elements returned from .values() will be discarded. You can then print them as follows:

for value in uniqueValues:  
    print(value)  
print(len(uniqueValues))

edited May 13 '19 at 07:46

answered Feb 18 '17 at 23:33

Joe Silverstein

406
5
7

This doesn't work if the values of myDict are dictionaries as well – Castor Dec 29 '21 at 00:32

Martijn Pieters · Answer 3 · 2013-06-20T16:21:09.150

Use a set():

from itertools import chain

unique_values = set(chain.from_iterable(d.values() for d in dictionaries_list))
for value in unique_values:
    print(value)

print(len(unique_values))

Use .itervalues() on Python 2 for a little more efficiency. Because you have a list of dictionaries, we need to pull out the values from each of those dictionaries first; I used itertools.chain.from_iterable() with a generator expression to list all values in a sequence:

>>> for value in set(chain.from_iterable(d.values() for d in dictionaries_list)):
...     print(value)
... 
news
sports
movies
music

The alternative is to use nested loops in the generator expression:

>>> for value in set(v for d in dictionaries_list for v in d.values()):
...     print(value)
... 
news
sports
movies
music

score 7 · Answer 4 · edited Oct 29 '18 at 13:56

7

dict = {'511':'Vishnu','512':'Vishnu','513':'Ram','514':'Ram','515':'sita'}
list =[] # create empty list
for val in dict.values(): 
  if val in list: 
    continue 
  else:
    list.append(val)

print list

edited Oct 29 '18 at 13:56

mthecreator

764
1
8
19

answered May 28 '16 at 06:13

Bala Subrahmanyam Balli

79
1
1

A `set` would be more efficient for this. Using the `in` operator is not as efficient for lists. – Andy Carlson Apr 09 '19 at 14:55

Print all Unique Values in a Python Dictionary

4 Answers4

Linked