I want to iterate through a dictionary in python by index number.
Example :
dict = {'apple':'red','mango':'green','orange':'orange'}
I want to iterate through the dictionary from first to last, so that I can access the dictionary items by their indexes. For example, the 1st item will be apple, and the 2nd item will be mango and value will be green.
Something like this:
for i in range(0,len(dict)):
dict.i
You can iterate over keys and get values by keys:
for key in dict.iterkeys():
print key, dict[key]
You can iterate over keys and corresponding values:
for key, value in dict.iteritems():
print key, value
You can use enumerate if you want indexes (remember that dictionaries don't have an order):
>>> for index, key in enumerate(dict):
... print index, key
...
0 orange
1 mango
2 apple
>>>
There are some very good answers here. I'd like to add the following here as well:
some_dict = {
"foo": "bar",
"lorem": "ipsum"
}
for index, (key, value) in enumerate(some_dict.items()):
print(index, key, value)
results in
0 foo bar
1 lorem ipsum
Appears to work with Python 2.7 and 3.5
I wanted to know (idx, key, value) for a python OrderedDict today (mapping of SKUs to quantities in order of the way they should appear on a receipt). The answers here were all bummers.
In python 3, at least, this way works and and makes sense.
In [1]: from collections import OrderedDict
...: od = OrderedDict()
...: od['a']='spam'
...: od['b']='ham'
...: od['c']='eggs'
...:
...: for i,(k,v) in enumerate(od.items()):
...: print('%d,%s,%s'%(i,k,v))
...:
0,a,spam
1,b,ham
2,c,eggs
Some of the comments are right in saying that these answers do not correspond to the question.
One reason one might want to loop through a dictionary using "indexes" is for example to compute a distance matrix for a set of objects in a dictionary. To put it as an example (going a bit to the basics on the bullet below):
This is why most packages use a condensed distance matrix ( How does condensed distance matrix work? (pdist) )
But consider the case one is implementing the computation of a distance matrix, or any kind of permutation of the sort. In such case you need to skip the results from more than half of the cases. This means that a FOR loop that runs through all the dictionary is just hitting an IF and jumping to the next iteration without performing really any job most of the time. For large datasets this additional "IFs" and loops add up to a relevant amount on the processing time and could be avoided if, at each loop, one starts one "index" further on the dictionary.
Going than to the question, my conclusion right now is that the answer is NO. One has no way to directly access the dictionary values by any index except the key or an iterator.
I understand that most of the answers up to now applies different approaches to perform this task but really don't allow any index manipulation, that would be useful in a case such as exemplified.
The only alternative I see is to use a list or other variable as a sequential index to the dictionary. Here than goes an implementation to exemplify such case:
#!/usr/bin/python3
dishes = {'spam': 4.25, 'eggs': 1.50, 'sausage': 1.75, 'bacon': 2.00}
print("Dictionary: {}\n".format(dishes))
key_list = list(dishes.keys())
number_of_items = len(key_list)
condensed_matrix = [0]*int(round(((number_of_items**2)-number_of_items)/2,0))
c_m_index = 0
for first_index in range(0,number_of_items):
for second_index in range(first_index+1,number_of_items):
condensed_matrix[c_m_index] = dishes[key_list[first_index]] - dishes[key_list[second_index]]
print("{}. {}-{} = {}".format(c_m_index,key_list[first_index],key_list[second_index],condensed_matrix[c_m_index]))
c_m_index+=1
The output is:
Dictionary: {'spam': 4.25, 'eggs': 1.5, 'sausage': 1.75, 'bacon': 2.0}
0. spam-eggs = 2.75
1. spam-sausage = 2.5
2. spam-bacon = 2.25
3. eggs-sausage = -0.25
4. eggs-bacon = -0.5
5. sausage-bacon = -0.25
Its also worth mentioning that are packages such as intertools that allows one to perform similar tasks in a shorter format.
Since you want to iterate in order, you can use sorted:
for k, v in sorted(dict.items()):
print k,v
When I need to keep the order, I use a list and a companion dict:
color = ['red','green','orange']
fruit = {'apple':0,'mango':1,'orange':2}
color[fruit['apple']]
for i in range(0,len(fruit)): # or len(color)
color[i]
The inconvenience is I don't get easily the fruit from the index. When I need it, I use a tuple:
fruitcolor = [('apple','red'),('mango','green'),('orange','orange')]
index = {'apple':0,'mango':1,'orange':2}
fruitcolor[index['apple']][1]
for i in range(0,len(fruitcolor)):
fruitcolor[i][1]
for f, c in fruitcolor:
c
Your data structures should be designed to fit your algorithm needs, so that it remains clean, readable and elegant.
There are several ways to call the for-loop in python and here what I found so far:
A = [1,2,3,4]
B = {"col1": [1,2,3],"col2":[4,5,6]}
# Forms of for loop in python:
# Forms with a list-form,
for item in A:
print(item)
print("-----------")
for item in B.keys():
print(item)
print("-----------")
for item in B.values():
print(item)
print("-----------")
for item in B.items():
print(item)
print("The value of keys is {} and the value of list of a key is {}".format(item[0],item[1]))
print("-----------")
Results are:
1
2
3
4
-----------
col1
col2
-----------
[1, 2, 3]
[4, 5, 6]
-----------
('col1', [1, 2, 3])
The value of keys is col1 and the value of list of a key is [1, 2, 3]
('col2', [4, 5, 6])
The value of keys is col2 and the value of list of a key is [4, 5, 6]
-----------
I can't think of any reason why you would want to do that. If you just need to iterate over the dictionary, you can just do.
for key, elem in testDict.items():
print key, elem
OR
for i in testDict:
print i, testDict[i]
