counting values in python

Question

How to count the number of occurrence of a values in a dictionary in python

a = dict()
a['cat'] =      1
a['fish'] =     1
a['dog'] =      2  
a['bat'] =      3
a['aardvark'] = 3
a['lion'] =    4  
a['wallaby'] =  5
a['badger'] =   5

output Expected:

EDIT

Sorry , i meant to say counting values

In a dictionaty, each key can occur at most once. The number of occurences can be determined by int(key in a), which returns 0 or 1. — Sven Marnach
– Sven Marnach, Commented Jul 2, 2012 at 12:55
What do you mean with number of occurence? (from a non-answer by Giorgos Komnino). — Martijn Pieters
– Martijn Pieters, Commented Jul 2, 2012 at 12:56
I'm sorry, but I find it very hard to figure out what you are asking here. It would help if you included some code to show what you have tried, it'll make it much easier for us to help you. Perhaps you could also take a look at whathaveyoutried.com for a great article on how to ask good questions? — Martijn Pieters
– Martijn Pieters, Commented Jul 2, 2012 at 13:03

Martijn Pieters · Accepted Answer · 2012-07-02 13:06:47Z

3

I suspect you want to use collections.Counter; it let's you handle most counting use cases with ease.

from collections import Counter
a = dict()
a['cat'] =      1
a['fish'] =     1
a['dog'] =      2  
a['bat'] =      3
a['aardvark'] = 3
a['lion'] =    4  
a['wallaby'] =  5
a['badger'] =   5

print Counter(a.values())

Output: Counter({1: 2, 3: 2, 5: 2, 2: 1, 4: 1})

Or, to format it a little for you:

for key, value in Counter(a.values()).most_common():
    print key, value

Output:

Or, to match your output exactly:

for key, value in sorted(Counter(a.values()).items()):
    print key, value

Here we sorted on the key (numbers 1 through 5).

edited Jul 2, 2012 at 13:06

answered Jul 2, 2012 at 12:58

Martijn Pieters

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3 Comments

Sven Marnach Over a year ago

That's not counting the number of occurrences of values in a dictionary, ist it?

Martijn Pieters Over a year ago

@SvenMarnach: No, but I think the OP doesn't know what he's asking.

Sven Marnach Over a year ago

Yeah, this kind of question is more about psychic skills than technical. :)

Ashwini Chaudhary · Accepted Answer · 2012-07-02 13:04:42Z

1

>>> from collections import Counter
>>> Counter(a.values())
Counter({1: 2, 3: 2, 5: 2, 2: 1, 4: 1})

edited Jul 2, 2012 at 13:04

answered Jul 2, 2012 at 12:58

Ashwini Chaudhary

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1 Comment

Rajeev Over a year ago

Hey Thanks..I should have been cleared when i stated the question initially..Had a long day at work :)

mgilson · Accepted Answer · 2012-07-02 13:05:40Z

1

a collections.Counter is the best tool for this job (see answer by Martijn Pieters) -- however, it was introduced in python 2.7. If you need a 2.5+ solution:

from collections import defaultdict
d=defaultdict(int)
for v in a.values():
    d[v]+=1

answered Jul 2, 2012 at 13:05

mgilson

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4 Comments

mgilson Over a year ago

@JonClements -- Because I didn't think of it. (I don't generally use the fact that int() returns 0). I'll update. (Thanks)

Martijn Pieters Over a year ago

Or use this backport of the Counter class instead.

Jon Clements Over a year ago

@MartijnPieters Or use setdefault etc... etc... - but think this one's been answered happily, but may have used our crystal balls out :)

Martijn Pieters Over a year ago

@JonClements: I'll see if I can polish up a spare one for future questions; my current one is surely cracked!

Jon Clements · Accepted Answer · 2012-07-02 13:01:41Z

0

I have a horrible feeling, and while it's unclear, that len(a) might be an answer...

However, it's also possible that:

from collections import Counter
Counter(a.values())

is also likely.

answered Jul 2, 2012 at 13:01

Jon Clements

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Comments

Lee Netherton · Accepted Answer · 2012-07-02 13:06:12Z

0

If you want the sum of the values do:

sum(a.values())

If you want the frequency of the number of occurrences do:

from collections import Counter
Counter(a.values()).items()

edited Jul 2, 2012 at 13:06

answered Jul 2, 2012 at 12:59

Lee Netherton

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Comments

Benedict · Accepted Answer · 2012-07-02 13:27:49Z

0

You can do this very easily without importing anything:

results={}
for v in a.values():
   results[v]=results.get(v, 0) + 1

for k,v in results.items():
    print k,v

Output:

answered Jul 2, 2012 at 13:27

Benedict

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