Assume a dictionary
d={'a':1,'b':2,'c':1}
When I use
d.keys()[d.values(). index(1)]
I get 'a',but i want get 'c' as well ,since the value of 'c' is also 1. How can i do that?
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3 Answers
You can use list comprehension, like this
print [key for key in d if d[key] == 1]
It iterates through the keys of the dictionary and checks if the value is 1. If the value is 1, it adds the corresponding key to the list.
Alternatively you can use, dict.iteritems() in Python 2.7, like this
print [key for key, value in d.iteritems() if value == 1]
In Python 3.x, you would do the same with dict.items(),
print([key for key, value in d.items() if value == 1])
Comments
For a one-shot, thefourtheye's answer is the most obvious and straightforward solution. Now if you need to lookup more than one value, you may want to build a "reverse index" instead:
from collections import defaultdict
def reverse(d):
r = defaultdict(list)
for k, v in d.items():
r[v].append(k)
return r
d={'a':1,'b':2,'c':1}
index = reverse(d)
print index[1]
=> ['a', 'c']
print index[2]
=> ['b']
answered Jul 25, 2014 at 14:54
bruno desthuilliers
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Comments
You can use the filter function to see all the keys in the dict that have the value you want.
d={'a':1,'b':2,'c':1}
x = filter(lambda k: d[k]==1, d.keys())
print x
['a', 'c']
I don't know if it is any more efficient than the manual loop; probably not. But it's more compact and clearer.
