CODEWITHSUNDEEP
pythonpython-2.7dictionaryindexingkey
chapter3
chapter3

Reputation: 994

How to get the index with the key in a dictionary?

I have the key of a python dictionary and I want to get the corresponding index in the dictionary. Suppose I have the following dictionary,

d = { 'a': 10, 'b': 20, 'c': 30}

Is there a combination of python functions so that I can get the index value of 1, given the key value 'b'?

d.??('b')

I know it can be achieved with a loop or lambda (with a loop embedded). Just thought there should be a more straightforward way.

Upvotes: 65

Views: 335538

Answers (7)

Ali Joghataee
Ali Joghataee

Reputation: 65

use list() alongside index()

b = {'a': 'a', 'b':'b', 'c':'c'}
print(list(b).index('a')

output:

0

Upvotes: -1

True Explorer
True Explorer

Reputation: 69

Convert your dict into a list first

d = { 'a': 10, 'b': 20, 'c': 30}
print(list(d.values())[1])
# OUTPUT: 20

Upvotes: -4

Martijn Pieters
Martijn Pieters

Reputation: 1125378

No, in Python 2 there is no straightforward way because dictionaries in that version do not have a set ordering (you need Python 3.6 or newer for that, 3.7 if it is not a cpython implementation).

From the documentation:

Keys and values are listed in an arbitrary order which is non-random, varies across Python implementations, and depends on the dictionary’s history of insertions and deletions.

In other words, the 'index' of b depends entirely on what was inserted into and deleted from the mapping before:

>>> map={}
>>> map['b']=1
>>> map
{'b': 1}
>>> map['a']=1
>>> map
{'a': 1, 'b': 1}
>>> map['c']=1
>>> map
{'a': 1, 'c': 1, 'b': 1}

As of Python 2.7, you could use the collections.OrderedDict() type instead, if insertion order is important to your application.

Upvotes: 3

Nick W.
Nick W.

Reputation: 1614

You can simply send the dictionary to list and then you can select the index of the item you are looking for.

DictTest = {
    '4000':{},
    '4001':{},
    '4002':{},
    '4003':{},
    '5000':{},
}

print(list(DictTest).index('4000'))

Upvotes: 3

Matt Alcock
Matt Alcock

Reputation: 12911

Dictionaries in python (<3.6) have no order. You could use a list of tuples as your data structure instead.

d = { 'a': 10, 'b': 20, 'c': 30}
newd = [('a',10), ('b',20), ('c',30)]

Then this code could be used to find the locations of keys with a specific value

locations = [i for i, t in enumerate(newd) if t[0]=='b']

>>> [1]

Upvotes: 5

Se7enstars
Se7enstars

Reputation: 37

#Creating dictionary
animals = {"Cat" : "Pat", "Dog" : "Pat", "Tiger" : "Wild"}

#Convert dictionary to list (array)
keys = list(animals)

#Printing 1st dictionary key by index
print(keys[0])

#Done :)

Upvotes: -1

Kiwisauce
Kiwisauce

Reputation: 1354

Use OrderedDicts: http://docs.python.org/2/library/collections.html#collections.OrderedDict

>>> x = OrderedDict((("a", "1"), ("c", '3'), ("b", "2")))
>>> x["d"] = 4
>>> x.keys().index("d")
3
>>> x.keys().index("c")
1

For those using Python 3

>>> list(x.keys()).index("c")
1

Upvotes: 107

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