Python Tuples dictionaries as keys select sort

Question

Suppose I have quantities of fruits of different colors  e g   24 blue bananas  12 green apples  0 blue strawberries and so on  I d like to organize them in a data structure in Python that allows for easy selection and sorting  My idea was to put them into a dictionary with tuples as keys  e g           banana       blue     24        apple        green    12        strawberry   blue     0               or even dictionaries  e g           fruit    banana       color    blue     24        fruit    apple        color    green    12        fruit    strawberry   color    blue     0               I d like to retrieve a list of all blue fruit  or bananas of all colors  for example  or to sort this dictionary by the name of the fruit  Are there ways to do this in a clean way  It might well be that dictionaries with tuples as keys are not the proper way to handle this situation  All suggestions welcome

User · Answer

Your best option will be to create a simple data structure to model what you have. Then you can store these objects in a simple list and sort/retrieve them any way you wish.

For this case, I'd use the following class:

class Fruit:
    def __init__(self, name, color, quantity): 
        self.name = name
        self.color = color
        self.quantity = quantity

    def __str__(self):
        return "Name: %s, Color: %s, Quantity: %s" % \
     (self.name, self.color, self.quantity)

Then you can simply construct "Fruit" instances and add them to a list, as shown in the following manner:

fruit1 = Fruit("apple", "red", 12)
fruit2 = Fruit("pear", "green", 22)
fruit3 = Fruit("banana", "yellow", 32)
fruits = [fruit3, fruit2, fruit1]

The simple list fruits will be much easier, less confusing, and better-maintained.

Some examples of use:

All outputs below is the result after running the given code snippet followed by:

for fruit in fruits:
    print fruit

Unsorted list:

Displays:

Name: banana, Color: yellow, Quantity: 32
Name: pear, Color: green, Quantity: 22
Name: apple, Color: red, Quantity: 12

Sorted alphabetically by name:

fruits.sort(key=lambda x: x.name.lower())

Displays:

Name: apple, Color: red, Quantity: 12
Name: banana, Color: yellow, Quantity: 32
Name: pear, Color: green, Quantity: 22

Sorted by quantity:

fruits.sort(key=lambda x: x.quantity)

Displays:

Name: apple, Color: red, Quantity: 12
Name: pear, Color: green, Quantity: 22
Name: banana, Color: yellow, Quantity: 32

Where color == red:

red_fruit = filter(lambda f: f.color == "red", fruits)

Displays:

Name: apple, Color: red, Quantity: 12

User · Answer

With keys as tuples  you just filter the keys with given second component and sort it   blue fruit   sorted  k for k in data keys   if k 1      blue    for k in blue fruit    print k 0   data k    prints  banana 24   etc   Sorting works because tuples have natural ordering if their components have natural ordering   With keys as rather full-fledged objects  you just filter by k color     blue     You can t really use dicts as keys  but you can create a simplest class like class Foo object   pass and add any attributes to it on the fly   k   Foo   k color    blue    These instances can serve as dict keys  but beware their mutability

User · Answer

You want to use two keys independently  so you have two choices    Store the data redundantly with two dicts as   banana      blue    4               and   blue     banana  4             Then  searching and sorting is easy but you have to make sure you modify the dicts together  Store it just one dict  and then write functions that iterate over them eg    d     banana      blue    4   yellow  6    apple    red  1     blueFruit     fruit d fruit   blue    if d fruit  has key  blue   for fruit in d keys

User · Answer

You could have a dictionary where the entries are a list of other dictionaries   fruit dict   dict   fruit dict  banana        yellow   24   fruit dict  apple        red   12     green   14   print fruit dict   Output        banana      yellow   24     apple      red   12     green   14      Edit   As eumiro pointed out  you could use a dictionary of dictionaries   fruit dict   dict   fruit dict  banana       yellow   24  fruit dict  apple       red   12   green   14  print fruit dict   Output        banana     yellow   24    apple       green   14   red   12

User · Answer

A dictionary probably isn t what you should be using in this case  A more full featured library would be a better alternative  Probably a real database  The easiest would be sqlite  You can keep the whole thing in memory by passing in the string   memory   instead of a filename   If you do want to continue down this path  you can do it with the extra attributes in the key or the value  However a dictionary can t be the key to a another dictionary  but a tuple can  The docs explain what s allowable  It must be an immutable object  which includes strings  numbers and tuples that contain only strings and numbers  and more tuples containing only those types recursively        You could do your first example with d      apple    red     4   but it ll be very hard to query for what you want  You d need to do something like this    find all apples apples    d key  for key in d keys   if key 0      apple     find all red items red    d key  for key in d keys   if key 1      red     the red apple redapples   d   apple    red

User · Answer

This type of data is efficiently pulled from a Trie-like data structure   It also allows for fast sorting  The memory efficiency might not be that great though   A traditional trie stores each letter of a word as a node in the tree   But in your case your  alphabet  is different   You are storing strings instead of characters   it might look something like this   root                 Root                                                                                    fruit        Banana Apple Strawberry                                                                color      Blue Yellow Green  Blue                                                                      end       24   100      12        0   see this link  trie in python

User · Answer

Database  dict of dicts  dictionary of list of dictionaries  named tuple  it s a subclass   sqlite  redundancy     I didn t believe my eyes  What else        It might well be that dictionaries with tuples as keys are not the proper way to handle this situation         my gut feeling is that a database is overkill for the OP s needs      Yeah  I thought  So  in my opinion  a list of tuples is plenty enough    from operator import itemgetter  li        banana        blue      24              apple         green     12              strawberry    blue      16               banana        yellow    13              apple         gold      3               pear          yellow    10              strawberry    orange    27              apple         blue      21              apple         silver    0               strawberry    green     4               banana        brown     14              strawberry    yellow    31              apple         pink      9               strawberry    gold      0               pear          gold      66              apple         yellow    9               pear          brown     5               strawberry    pink      8               apple         purple    7               pear          blue      51              chesnut       yellow    0         print set  u 1  for u in li      all potential colors  print set  c for f c n in li if n  0     all effective colors  print   c for f c n in li if f   banana       all potential colors of bananas  print   c for f c n in li if f   banana  and n  0     all effective colors of bananas  print  print set  u 0  for u in li      all potential fruits  print set  f for f c n in li if n  0     all effective fruits  print   f for f c n in li if c   yellow       all potential fruits being yellow  print   f for f c n in li if c   yellow  and n  0     all effective fruits being yellow  print  print len set  u 1  for u in li       number of all potential colors  print len set c for f c n in li if n  0      number of all effective colors  print len   c for f c n in li if f   strawberry       number of potential colors of strawberry  print len   c for f c n in li if f   strawberry  and n  0      number of effective colors of strawberry  print    sorting li by name of fruit print sorted li     sorted li by name of fruit  print    sorting li by number  print sorted li  key   itemgetter 2      sorted li by number  print    sorting li first by name of color and secondly by name of fruit print sorted li  key   itemgetter 1 0      sorted li first by name of color and secondly by name of fruit  print   result  set   blue    brown    gold    purple    yellow    pink    green    orange    silver      all potential colors set   blue    brown    gold    purple    yellow    pink    green    orange      all effective colors   blue    yellow    brown     all potential colors of bananas   blue    yellow    brown     all effective colors of bananas  set   strawberry    chesnut    pear    banana    apple      all potential fruits set   strawberry    pear    banana    apple      all effective fruits   banana    pear    strawberry    apple    chesnut     all potential fruits being yellow   banana    pear    strawberry    apple     all effective fruits being yellow  9   number of all potential colors 8   number of all effective colors 6   number of potential colors of strawberry 5   number of effective colors of strawberry     apple    blue   21     apple    gold   3     apple    green   12     apple    pink   9     apple    purple   7     apple    silver   0     apple    yellow   9     banana    blue   24     banana    brown   14     banana    yellow   13     chesnut    yellow   0     pear    blue   51     pear    brown   5     pear    gold   66     pear    yellow   10     strawberry    blue   16     strawberry    gold   0     strawberry    green   4     strawberry    orange   27     strawberry    pink   8     strawberry    yellow   31     sorted li by name of fruit     apple    silver   0     strawberry    gold   0     chesnut    yellow   0     apple    gold   3     strawberry    green   4     pear    brown   5     apple    purple   7     strawberry    pink   8     apple    pink   9     apple    yellow   9     pear    yellow   10     apple    green   12     banana    yellow   13     banana    brown   14     strawberry    blue   16     apple    blue   21     banana    blue   24     strawberry    orange   27     strawberry    yellow   31     pear    blue   51     pear    gold   66     sorted li by number     apple    blue   21     banana    blue   24     pear    blue   51     strawberry    blue   16     banana    brown   14     pear    brown   5     apple    gold   3     pear    gold   66     strawberry    gold   0     apple    green   12     strawberry    green   4     strawberry    orange   27     apple    pink   9     strawberry    pink   8     apple    purple   7     apple    silver   0     apple    yellow   9     banana    yellow   13     chesnut    yellow   0     pear    yellow   10     strawberry    yellow   31     sorted li first by name of color and secondly by name of fruit

User · Answer

Personally  one of the things I love about python is the tuple-dict combination  What you have here is effectively a 2d array  where x   fruit name and y   color   and I am generally a supporter of the dict of tuples for implementing 2d arrays  at least when something like numpy or a database isn t more appropriate  So in short  I think you ve got a good approach   Note that you can t use dicts as keys in a dict without doing some extra work  so that s not a very good solution    That said  you should also consider namedtuple    That way you could do this    gt  gt  gt  from collections import namedtuple  gt  gt  gt  Fruit   namedtuple  Fruit     name    color     gt  gt  gt  f   Fruit name  banana   color  red    gt  gt  gt  print f Fruit name  banana   color  red    gt  gt  gt  f name  banana   gt  gt  gt  f color  red    Now you can use your fruitcount dict    gt  gt  gt  fruitcount    Fruit  banana    red   5   gt  gt  gt  fruitcount f  5   Other tricks    gt  gt  gt  fruits   fruitcount keys    gt  gt  gt  fruits sort    gt  gt  gt  print fruits  Fruit name  apple   color  green      Fruit name  apple   color  red      Fruit name  banana   color  blue      Fruit name  strawberry   color  blue     gt  gt  gt  fruits sort key lambda x x color   gt  gt  gt  print fruits  Fruit name  banana   color  blue      Fruit name  strawberry   color  blue      Fruit name  apple   color  green      Fruit name  apple   color  red      Echoing chmullig  to get a list of all colors of one fruit  you would have to filter the keys  i e    bananas    fruit for fruit in fruits if fruit name   banana

[python] Python: Tuples/dictionaries as keys, select, sort

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