Sort a list(tuple,dict)

FROM:https://www.pythoncentral.io/how-to-sort-python-dictionaries-by-key-or-value/

AND https://www.pythoncentral.io/how-to-sort-a-list-tuple-or-object-with-sorted-in-python/

The dict (dictionary) class object in Python is a very versatile and useful container type, able to store a collection of values and retrieve them via keys.

numbers = {'first': 1, 'second': 2, 'third': 3, 'Fourth': 4}

>>> sorted(numbers)

['Fourth', 'first', 'second', 'third']

 

>>> sorted(numbers.values())

[1, 2, 3, 4]

 

>>> sorted(numbers, key=numbers.__getitem__)

# In order of sorted values: [1, 2, 3, 4]

['first', 'second', 'third', 'Fourth']

 

# Uses the first element of each tuple to compare

>>> [value for (key, value) in sorted(numbers.items())]

[4, 1, 2, 3]

# In order of sorted keys: ['Fourth', 'first', 'second', 'third']

 

>>> sorted(numbers, key=numbers.__getitem__, reverse=True)

['Fourth', 'third', 'second', 'first']

>>> [value for (key, value) in sorted(numbers.items(), reverse=True)]

[3, 2, 1, 4]

reverse 标识若为true，顺序为反向排序

 

# Won't change the items to be returned, only while sorting

>>> sorted(numbers, key=str.lower)

['first', 'Fourth', 'second', 'third']

 

>>> month = dict(one='January',

                 two='February',

                 three='March',

                 four='April',

                 five='May')

>>> numbermap = {'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5}

>>> sorted(month, key=numbermap.__getitem__)

['one', 'two', 'three', 'four', 'five']

同时我们可以对一些字典进行利用一些赋值的数据进行权值排序

 

# Assuming the keys in both dictionaries are EXACTLY the same:

>>> [month[i] for i in sorted(month, key=numbermap.__getitem__)]

['January', 'February', 'March', 'April', 'May']

 

 If we wanted to sort our key/value strings by the number of repeated letters in each string, we could define our own custom method to use in the sorted key argument:

 

def repeats(string):

    # Lower the case in the string

    string = string.lower()

 

    # Get a set of the unique letters

    uniques = set(string)

 

    # Count the max occurrences of each unique letter

    counts = [string.count(letter) for letter in uniques]

 

    return max(counts)

 

# From greatest to least repeats

>>> sorted(month.values(), key=repeats, reverse=True)

['February', 'January', 'March', 'April', 'May']

More advanced sorting functionality

def evens1st(num):

    # Test with modulus (%) two

    if num == 0:

        return -2

    # It's an even number, return the value

    elif num % 2 == 0:

        return num

    # It's odd, return the negated inverse

    else:

        return -1 * (num ** -1)

 

# Max class size first

>>> sorted(trans.values(), key=evens1st, reverse=True)

[30, 24, 33, 7, 0]

Sorting a List(or Tuple) of Custom Python Objects

class Custom(object):

    def __init__(self, name, number):

        self.name = name

        self.number = number

 

    def __repr__(self):

        return '{}: {} {}'.format(self.__class__.__name__,

                                  self.name,

                                  self.number)

def getKey(custom):

    return custom.number

 

>>> sorted(customlist, key=getKey)

[Custom: michael 1, Custom: life 42,

Custom: theodore the great 59, Custom: object 99]

 

Or maybe you feel it's nit-picking,and don't want to type the key keyword everytime,

Redifine our project one more time like this

 

class Custom(object):

    def __init__(self, name, number):

        self.name = name

        self.number = number

 

    def __repr__(self):

        return '{}: {} {}'.format(self.__class__.__name__,

                                  self.name,

                                  self.number)

 

    def __cmp__(self, other):

        if hasattr(other, 'number'):

            return self.number.__cmp__(other.number)

 

>>> sorted(customlist)

[Custom: michael 1, Custom: life 42, Custom: theodore the great 59, Custom: object 99]

Sorting a Heterogeneous List of Custom Python Objects

class AnotherObject(object):

    def __init__(self, tag, age, rate):

        self.tag = tag

        self.age = age

        self.rate = rate

    def __repr__(self):

        return '{}: {} {} {}'.format(self.__class__.__name__,

                                     self.tag,

                                     self.age, self.rate)

    def __cmp__(self, other):

        if hasattr(other, 'age'):

            return self.age.__cmp__(other.age)

customlist = [

    Custom('object', 99),

    Custom('michael', 1),

    Custom('theodore the great', 59),

    Custom('life', 42),

    AnotherObject('bananas', 37, 2.2),

    AnotherObject('pants', 73, 5.6),

    AnotherObject('lemur', 44, 9.2)

]

try it,and ...error:

>>> sorted(customlist)

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: an integer is required

 

Why? Because Custom doesn't have an attribute called age and AnotherObject doesn't have an attribute called number.

Let's redefine those objects again!

class Custom(object):

    def __init__(self,name,number):

        self.name = name

        self.number = number

 

    def __repr__(self):

        return '{}: {} {}'.format(self.__class__.__name__,

                                  self.name,

                                  self.number)

 

    def __cmp__(self, other):

        if hasattr(other, 'getKey'):

            return self.getKey().__cmp__(other.getKey())

 

    def getKey(self):

        return self.number

 

 

class AnotherObject(object):

    def __init__(self, tag, age, rate):

        self.tag = tag

        self.age = age

        self.rate = rate

 

    def __repr__(self):

        return '{}: {} {} {}'.format(self.__class__.__name__,

                                     self.tag,

                                     self.age, self.rate)

 

    def __cmp__(self, other):

        if hasattr(other, 'getKey'):

            return self.getKey().__cmp__(other.getKey())

 

    def getKey(self):

        return self.age

>>> sorted(customlist)

[Custom: michael 1, AnotherObject: bananas 37 2.2,

Custom: life 42, AnotherObject: lemur 44 9.2,

Custom: theodore the great 59, AnotherObject: pants 73 5.6,

Custom: object 99]

And it finally Success

 

You can do that too. If you leave out the __cmp__ functions in each object, and define an outside function like so:

def getKey(customobj):

    return customobj.getKey()\

And then call sorted like so:

>>> sorted(customlist, key=getKey)

[Custom: michael 1, AnotherObject: bananas 37 2.2,

Custom: life 42, AnotherObject: lemur 44 9.2,

Custom: theodore the great 59, AnotherObject: pants 73 5.6,

Custom: object 99]