Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-28 Thread Lie Ryan 
Message: 8
Date: Thu, 31 Jul 2008 20:16:54 -0700 (PDT)
From: Angela Yang [EMAIL PROTECTED]
Subject: [Tutor] how do I create a lists of values associated with a
   key?
To: tutor@python.org
Message-ID: [EMAIL PROTECTED]
Content-Type: text/plain; charset=iso-8859-1


 That did not work because list index is not numeric.

Dictionary is an unordered set (list is an ordered set) indexed by a
immutable value (e.g. string, numbers, tuple)

 But for dictionaries, it is key - value pairs.? But I need key - multiple
values.

That would mean, a dictionary of lists. Dictionary keys cannot be a mutable
(i.e. list cannot be a dictionary key) but dictionary's value may be
mutable.
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[Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Angela Yang 
Hi,



I have a list of values for one key.  How do I specify this data structure?



First tried,



collection = []

collection['abby'].append('apprentice1')

collection['abby'].append('apprentice2')



That did not work because list index is not numeric.

But for dictionaries, it is key - value pairs.  But I need key - multiple 
values.



Do you have some example how to specify this?



Angela








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Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Marc Tompkins 
On Thu, Jul 31, 2008 at 8:16 PM, Angela Yang [EMAIL PROTECTED] wrote:

 Hi,

 I have a list of values for one key.  How do I specify this data structure?

 First tried,

 collection = []
 collection['abby'].append('apprentice1')
 collection['abby'].append('apprentice2')

 That did not work because list index is not numeric.
 But for dictionaries, it is key - value pairs.  But I need key - multiple
 values.

 Do you have some example how to specify this?

 Angela


Each value can, itself, be a container - a tuple, a list, or another
dictionary.

dictTuple = {a:(1,2,3), b:(4,5,6)}
dictList = {a:[1,2,3], b:[4,5,6]}
dictDict = {a:{c:1,d:2,e:3}, b:{f:4,g:5,h:6}}

Retrieving values:
valValue = dictTuple[a][0]  # 1
valValue = dictTuple[b][2]  # 6

Lists work just the same:
valValue = dictList[a][0]  # 1
valValue = dictList[b][2]  # 6

Dictionaries are, well, like dictionaries:
valValue = dictDict[a][c]  # 1
valValue = dictDict[b][h]  # 6


Hope that helps

-- 
www.fsrtechnologies.com
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Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Alan Gauld 


Angela Yang [EMAIL PROTECTED] wrote

But for dictionaries, it is key - value pairs. But I need key - 
multiple values.


But a value can be a list.

d = {}
d['odd'] = [1,3,5,7]
d['even'] = [2,4,6,8]

print d['odd'][2]# = 5


See the Raw Materials top[ic in my tutorial for another
example using a dictionary to store address data:


addressBook = {

... 'Fred' : ['Fred', '9 Some St',' Anytown', '0123456789'],
... 'Rose' : ['Rose', '11 Nother St', 'SomePlace', '0987654321']
... } print addressBook['Rose']
['Rose', '11 Nother St', 'SomePlace', '0987654321']

print addressBook['Fred'][3]

0123456789
HTH,


--
Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld 



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Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Benoit Thiell 

Dear Angela,

in order to do this, the setdefault function of the dictionaries is very 
useful.


For example:
mydict = {}
mylist = mydict.setdefault(mykey, [])
mylist.append(myvalue)

setdefault either returns the already existing list or sets a new list 
for the key and returns it.


Regards,
Benoit Thiell.

On Fri, 1 Aug 2008, Marc Tompkins wrote:




On Thu, Jul 31, 2008 at 8:16 PM, Angela Yang [EMAIL PROTECTED] wrote:
  Hi,

  I have a list of values for one key.  How do I specify this data 
structure?

  First tried,

  collection = []
  collection['abby'].append('apprentice1')
  collection['abby'].append('apprentice2')

  That did not work because list index is not numeric.
  But for dictionaries, it is key - value pairs.  But I need key - 
multiple values.

  Do you have some example how to specify this?

  Angela


Each value can, itself, be a container - a tuple, a list, or another 
dictionary.

dictTuple = {a:(1,2,3), b:(4,5,6)}
dictList = {a:[1,2,3], b:[4,5,6]}
dictDict = {a:{c:1,d:2,e:3}, b:{f:4,g:5,h:6}}

Retrieving values:
valValue = dictTuple[a][0]  # 1
valValue = dictTuple[b][2]  # 6

Lists work just the same:
valValue = dictList[a][0]  # 1
valValue = dictList[b][2]  # 6

Dictionaries are, well, like dictionaries:
valValue = dictDict[a][c]  # 1
valValue = dictDict[b][h]  # 6


Hope that helps

--
www.fsrtechnologies.com

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Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Kent Johnson 
On Thu, Jul 31, 2008 at 11:16 PM, Angela Yang [EMAIL PROTECTED] wrote:
 Hi,

 I have a list of values for one key.  How do I specify this data structure?

 First tried,

 collection = []
 collection['abby'].append('apprentice1')
 collection['abby'].append('apprentice2')

 That did not work because list index is not numeric.
 But for dictionaries, it is key - value pairs.  But I need key - multiple
 values.

A dict or defaultdict  with list values would work well here. The
defaultdict has the advantage of not requiring any user code to handle
missing keys:

In [7]: from collections import defaultdict
In [8]: c=defaultdict(list)
In [9]: c['abby'].append('apprentice1')
In [10]: c['abby'].append('apprentice2')
In [11]: c
Out[11]: defaultdict(type 'list', {'abby': ['apprentice1', 'apprentice2']})

Kent
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Re: [Tutor] how do I create a lists of values associated with a key?

2008-08-01 Thread Monika Jisswel 
2008/8/1 Angela Yang [EMAIL PROTECTED]


 collection = []
 collection['abby'].append('apprentice1')
 collection['abby'].append('apprentice2')

 That did not work because list index is not numeric.
 But for dictionaries, it is key - value pairs.  But I need key - multiple 
 values.

 Do you have some example how to specify this?


You already know this :
Collection1 = []
Collection2 = []
Collection1.append('apprentice1')
Collection1.append('apprentice2')

if you add a MainCollection to the picture which can be coded like this:
MainCollection = {'Collection1':[], 'Collection2':[]}
Adding elements to a Collection is as simple as this interactive
session demonstrates :

Python 2.4.4 (#2, Apr 15 2008, 23:43:20)
[GCC 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)] on linux2
Type help, copyright, credits or license for more information.


 MainCollection = {'Collection1':[], 'Collection2':[]}
 type(MainCollection)
type 'dict'
 MainCollection['Collection1']
[]
 MainCollection['Collection1'].append('aa')
 MainCollection['Collection1']
['aa']
 MainCollection['Collection1'].append('bb')
 MainCollection['Collection1']
['aa', 'bb']
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