CODEWITHSUNDEEP
pythondictionary
user7172
user7172

Reputation: 974

Sum values in a Python dict?

How to sum the values in a python dict when I add the same key?

d = {'key1':10,'key2':14,'key3':47}
d['key1'] = 20

After the above the value of d['key1'] should be 30.

Is this possible?

Upvotes: 1

Views: 614

Answers (4)

Harshit Agarwal
Harshit Agarwal

Reputation: 908

d = {'key1':10,'key2':14,'key3':47}

Solution in One line to sum the values in a python dict when we add the same key:

d['key1'] = dict.get('key1', 0) + 20

Explanation:

dict.get('key1', 0)

this will return the the key value if found in dict otherwise return default value as 0

Upvotes: 0

Kimvais
Kimvais

Reputation: 39638

from collections import defaultdict
d = defaultdict(int)
d['key1'] += 20

Upvotes: 4

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 251196

You can use collections.Counter:

>>> from collections import Counter
>>> d =Counter()
>>> d.update({'key1':10,'key2':14,'key3':47})
>>> d['key1'] += 20
>>> d['key4'] += 50  # Also works for keys that are not present
>>> d
Counter({'key4': 50, 'key3': 47, 'key1': 30, 'key2': 14})

Counter has some advantages:

>>> d1 = Counter({'key4': 50, 'key3': 4})
#You can add two counters
>>> d.update(d1)
>>> d
Counter({'key4': 100, 'key3': 51, 'key1': 30, 'key2': 14})

You can get a list of sorted items(based on the value) using most_common():

>>> d.most_common()
[('key4', 100), ('key3', 51), ('key1', 30), ('key2', 14)]

Timing comparisons:

>>> keys = [ random.randint(0,1000) for _ in xrange(10**4)]
>>> def dd():                             
    d = defaultdict(int)
    for k in keys:
        d[k] += 10
...         
>>> def count():                             
    d = Counter()
    for k in keys:
        d[k] += 10
...         
>>> def simple_dict():
...     d = {}
...     for k in keys:
...         d[k] = d.get(k,0) + 10
...         
>>> %timeit dd()
100 loops, best of 3: 3.47 ms per loop
>>> %timeit count()
100 loops, best of 3: 10.1 ms per loop
>>> %timeit simple_dict()
100 loops, best of 3: 5.01 ms per loop

Upvotes: 5

tusharmakkar08
tusharmakkar08

Reputation: 706

try:
   dict[key1]+=20 #The value you wanted
except KeyError:
   dict[key1]=10 #The initial Value

Upvotes: 0

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