How do I reverse the order of key-value pairs of a dictionary, in Python? For example, I have this dictionary:
{"a":1, "b":2, "c":3}
I want to reverse it so that it returns:
{"c":3, "b":2, "a":1}
Is there a function that I haven't heard about that can do this? Some lines of code is fine as well.
Dictionary does not have any sense of order , so your key/value pairs are not ordered in any format.
If you want to preserve the order of the keys, you should use collections.OrderedDict from the start, instead of using normal dictionary , Example -
>>> from collections import OrderedDict
>>> d = OrderedDict([('a',1),('b',2),('c',3)])
>>> d
OrderedDict([('a', 1), ('b', 2), ('c', 3)])
OrderedDict would preserve the order in which the keys were entered into the dictionary. In above case, it would be the order in which the keys existed in the list - [('a',1),('b',2),('c',3)] - 'a' -> 'b' -> 'c'
Then you can get the reversed order of keys using reversed(d) , Example -
>>> dreversed = OrderedDict()
>>> for k in reversed(d):
... dreversed[k] = d[k]
...
>>> dreversed
OrderedDict([('c', 3), ('b', 2), ('a', 1)])
#The dictionary to be reversed
dict = {"key1":"value1","key2":"value2","key3":"value3"}
#Append the keys of the dictionary in a list
list_keys = []
for k in dict.keys():
list_keys.append(k)
rev_dict = {}
#Traverse through the reversed list of keys and add them to a new dictionary
for i in reversed(list_keys):
rev_dict[i] = dict[I]
print(rev_dict)
#OUTPUT: {'key3': 'value3', 'key2': 'value2', 'key1': 'value1'}
A dictionary uses Hashmap to store Key and corresponding values.
Look at : Is a Python dictionary an example of a hash table?
Anything related to hash has no order.
You can do it with this:
d = {}
d['a']=1
d['b']=2
d['c']=3
d['d']=4
print d
for k,v in sorted(d.items(),reverse = True):
print k,v
d.items() returns a list of tuples : [('a', 1), ('c', 3), ('b', 2), ('d', 4)] and k,v gets the values in tuples to iterate in loop.
sorted() returns a sorted list, whereas you cannot use d.items().sort() which does not return, but instead tries to overwrite the d.items().
This will work. Based on Venkateshwara's that didn't work for me 'as is'.
def reverse(self):
a = self.yourdict.items()
b = list(a) # cast to list from dict_view
b.reverse() # actual reverse
self.yourdict = dict(b) # push back reversed values
d={"a":1, "b":2, "c":3}
x={}
for i in sorted(d.keys(),reverse=True):
x[i]=d[i]
print(x)
