Can python dictionaries be sorted?

In python, dictionary is a built-in data type, an unordered storage structure, and each element is a key-value pair.

For example: dict = {'username': 'xiaoming', 'password': '123456'}, where 'username' and 'password' are keys, and ' Xiaoming' and '123456' are values. You can get the reference to the corresponding value value through d[key], but you cannot get the key through value.

For dictionnary, you need to know the following points:

a. The key of dictionary is case-sensitive;

b. A dictionary There cannot be duplicate keys;

c. Dictionaries are unordered and have no concept of element order. They are just simple arrangements of order pairs.

Dictionary is sorted by key/value:

The dictionary itself has no concept of order, but it is always at some point, but we often need to Dictionary sorting

Method 1: Sort by key value.

def sortedDictValues1(adict):
    items = adict.items()
    print "items:",items 
    items.sort()
    return [value for key, value in items]
adict = {"a1":11,"b1":2,"c1":30,"e1":20,"d1":4}
print sortedDictValues1(adict)
items: [('a1', 11), ('c1', 30), ('e1', 20), ('b1', 2), ('d1', 4)]
[11, 2, 30, 4, 20]

The items method of the dictionary returns a list of tuples, each tuple containing a pair of items - a key and a corresponding value. A list of tuples can be sorted using the sort() method.

Method 2: Sort by key value

def sortedDictValues2(adict): 
    keys = adict.keys() 
    keys.sort() 
    return [dict[key] for key in keys]

The keys() method of the dictionary object returns a list of all key values ​​in the dictionary, and the order is random. When you need to sort, just use the sort() method on the returned key value list, which is faster than method 1.

Method 3: Sort by key value

def sortedDictValues3(adict): 
    keys = adict.keys() 
    keys.sort() 
    return map(adict.get, keys)

Use the mapping method to perform the last step more efficiently

Method 4: One line Statement

[(k,di[k]) for k in sorted(di.keys())]

Method 5: Sort by value

def sort_by_value(d): 
    items=d.items() 
    backitems=[[v[1],v[0]] for v in items] 
    backitems.sort() 
    return [ backitems[i][1] for i in range(0,len(backitems))]

First exchange the key and value positions of the item into a list, and then according to each list The first value of the element, that is, the original value, sorted:

Method 6: Sort by value

[ v for v in sorted(di.values())]

Method 7: Use the sorted function key= parameter sorting:

Sort by key

print sorted(dict1.items(), key=lambda d: d[0])

Sort by value

print sorted(dict1.items(), key=lambda d: d[1])
python内置sorted函数的帮助文档：
sorted(…)
sorted(iterable, cmp=None, key=None, reverse=False) –> new sorted list

The method of sorting dictionary, in fact, their core ideas are the same, that is, dictionary The elements in are separated into a list, and the list is sorted, thereby indirectly sorting the dictionary. This "element" can be key, value or item.

Method 8: PYTHON's COLLECTION series - ordered dictionary (ORDEREDDICT)

orderdDict is a supplement to the dictionary type, which retains the order in which dictionary elements are added

import collections
dic = collections.OrderedDict()
dic["featureName"] = "f1"
dic["uId"] = "12345"
dic["value"] = "7"
print dic
#结果
#OrderedDict([('featureName', 'f1'), ('uId', '12345'), ('value', '7')])

The above is the detailed content of Can python dictionaries be sorted?. For more information, please follow other related articles on the PHP Chinese website!