How to reverse order of keys in python dict?
This is my code :
a = {0:'000000',1:'11111',3:'333333',4:'444444'}
for i in a:
print i
it shows:
0
1
3
4
but I want it开发者_运维百科 to show:
4
3
1
0
so, what can I do?
Note: this answer is only true for Python < 3.7. Dicts are insertion ordered starting in 3.7 (and CPython 3.6 as an implementation detail).
The order keys are iterated in is arbitrary. It was only a coincidence that they were in sorted order.
>>> a = {0:'000000',1:'11111',3:'333333',4:'444444'}
>>> a.keys()
[0, 1, 3, 4]
>>> sorted(a.keys())
[0, 1, 3, 4]
>>> reversed(sorted(a.keys()))
<listreverseiterator object at 0x02B0DB70>
>>> list(reversed(sorted(a.keys())))
[4, 3, 1, 0]
Since Python 3.7, dicts preserve order, which means you can do this now:
my_dict = {'a': 1, 'c': 3, 'b': 2}
for k in reversed(list(my_dict.keys())):
print(k)
Output:
b
c
a
Since Python 3.8, the built-in function reversed()
accepts dicts as well.
Here's an example of how you can use it to iterate:
my_dict = {'a': 1, 'c': 3, 'b': 2}
for k in reversed(my_dict):
print(k)
Here's an example of how you can replace your dict with a reversed dict:
my_dict = dict(reversed(my_dict.items()))
Dictionaries are unordered so you cannot reverse them. The order of the current output is arbitrary.
That said, you can order the keys of course:
for i in sorted(a.keys(), reverse=True):
print a[i];
but this gives you the reverse order of the sorted keys, not necessarily the reverse order of the keys how they have been added. I.e. it won't give you 1 0 3
if your dictionary was:
a = {3:'3', 0:'0', 1:'1'}
Try:
for i in sorted(a.keys(), reverse=True):
print i
Python dict is not ordered in 2.x. But there's an ordered dict implementation in 3.1.
Python dictionaries don't have any 'order' associated with them. It's merely a 'coincidence' that the dict is printing the same order. There are no guarantees that items in a dictionary with come out in any order.
If you want to deal with ordering you'll need to convert the dictionary to a list.
a = list(a) # keys in list
a = a.keys() # keys in list
a = a.values() # values in list
a = a.items() # tuples of (key,value) in list
Now you can sort the list as normal, e.g., a.sort()
and reverse it as well, e.g., a.reverse()
In Python 3.6, which I am using, I reversed the order of keys with their respective values with the help of function update.
original_dict={'A':0,'C':2,'B':1}
new_dict={}
for k,v in original_dict.items():
dict_element={k:v}
dict_element.update(new_dict)
new_dict=dict_element
print(new_dict)
It should print out:
{'B':1,'C':2,'A':0}
My 2 ¢.
If you want to preserve the insertion order and not the alphabetical ordering, then you can use:
dict(list(your_dict.keys())[::-1])
Or for the whole dictionary:
dict(list(your_dict.items())[::-1])
for i in reversed(sorted(a.keys())):
print i
If you have a dictionary like this
{'faisal2': 2, 'umair': 2, 'fais': 1, 'umair2': 1, 'trending': 2, 'apple': 2, 'orange': 2}
and you want to reverse sort dictionary you can use:
dict(sorted(counts.items(), key=lambda item: item[1],reverse=True))
output will be:
{'faisal2': 2, 'umair': 2, 'trending': 2, 'apple': 2, 'orange': 2, 'fais': 1, 'umair2': 1}
just try,
INPUT: a = {0:'000000',1:'11111',3:'333333',4:'444444'}
[x for x in sorted(a.keys(), reverse=True)]
OUTPUT: [4, 3, 1, 0]
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