python : How to create a list of all the keys in the Dictionary ?
In this article we will discuss how to create a list of all keys in a dictionary.
Suppose we have a dictionary of string and integers i.e.
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# Dictionary of string and int wordFreqDic = { "Hello": 56, "at" : 23 , "test" : 43, "this" : 78, "here" : 18, "city" : 2, } |
Now how to get all the keys from above dictionary in a list i.e.
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['city', 'test', 'at', 'Hello', 'this', 'here'] |
Creating a list of all keys in dictionary using dict.keys()
In python, dictionary class provides a member function i.e.
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dict.keys() |
It returns a view object or iterator to the list of all keys in dictionary. We can use this object for iteration or creating new list. Let’s use that to get the list of all keys in the above dictionary.
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# Create a new list from the view object returned by keys() dictkeys = list (wordFreqDic.keys()) |
dictkeys content will be,
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['city', 'test', 'at', 'Hello', 'this', 'here'] |
Creating a filtered list of dictionary keys using List Comprehension
Suppose from above mentioned dictionary, we want a list of keys that start with character ‘t’ only i.e.
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['test', 'this'] |
let’s do that using for loop i.e.
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dictkeys = list() # Creating a list of keys that start with 't' for x in wordFreqDic : if x.startswith('t') : dictkeys.append(x) |
dictkeys content will be,
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['test', 'this'] |
But that’s not pythonic. Let’s do that using list comprehension,
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# Creating a list of keys that start with 't' dictkeys = [x for x in wordFreqDic if x.startswith('t')] |
dictkeys content will be,
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['test', 'this'] |
Further Learning,
Complete example is as follows,
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def main(): # Dictionary of string and int wordFreqDic = { "Hello": 56, "at" : 23 , "test" : 43, "this" : 78, "here" : 18, "city" : 2, } print("Dictionary : ", wordFreqDic) ''' Creating a list of keys in dictionary ''' # Create a new list from the view object returned by keys() dictkeys = list (wordFreqDic.keys()) print("List of keys in Dictionary : ", dictkeys) ''' Creating a filtered list of keys in dictionary using for loop ''' dictkeys = list() # Creating a list of keys that start with 't' for x in wordFreqDic : if x.startswith('t') : dictkeys.append(x) print("List of keys in Dictionary that start with 't' : " , dictkeys) ''' Creating a filtered list of keys in dictionary using List comprehension ''' # Creating a list of keys that start with 't' dictkeys = [x for x in wordFreqDic if x.startswith('t')] print("List of keys in Dictionary that start with 't' : " , dictkeys) if __name__ == '__main__': main() |
Output:
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Dictionary : {'city': 2, 'test': 43, 'at': 23, 'Hello': 56, 'this': 78, 'here': 18} List of keys in Dictionary : ['city', 'test', 'at', 'Hello', 'this', 'here'] List of keys in Dictionary that start with 't' : ['test', 'this'] List of keys in Dictionary that start with 't' : ['test', 'this'] |
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