Re: Multiple values for one key

[norseman]

Terry Reedy wrote:

>
>
Ron Brennan wrote:

>Hello,
>>
>>
>How would I create a dictionary that contains multiple values for one
>key.

>
Make the value a collection object (set or list if you plan to add and
delete).
>

> I'd also like the key to be able to have duplicate entries.

>
Dict keys must be hashable and unique.
>
tjr
>
--

http://mail.python.org/mailman/listinfo/python-list

>

=============== =
First part I understand, second is still giving me a problem.

For some reason I still want keys to be dbf column headers.
like:

name:address:zi p so forth
---- ------- --- ------------------
guy: unknown:00000
girl: 123 tiny street:12345
boy:321 here:33333
gal:999 over there: 55555
so forth

Thus one key has many values. And you can then index on whatever key(s)
you wish - name,zip...

With billions plus records, trying to put a unique key on each entry
seems to preclude the need for a dictionary, just use the entries.
(Format to SDF and index on substr(line,1,2 4)+substr(line, 48,+5) etc..)
name + zip
OK - I know I missed the whole concept of a Python Dictionary. I haven't
read anything as yet that gives a clear picture of what it is and what
it is for. Please, classroom concepts usually consist of a handful of
objects. I have files here that takes up multiple DVDs each, AFTER a 15
to 1 compression. 3 bytes per pixel. I need to work with them. Things
like changing geobase projections and cookie cutting based on real world
coordinates and modifying the lumens and so forth. Based on what I've
read, the Python Dictionary concept flat will not work for such as this.
Yes - the example is overkill. But in my world it is reality. I deal
with sizeable things. Not all are raster. Most all are binary! Things
that work on massive text files - like banking and mortgage - simply
don't work here. There are seldom 'lines'. There are always bytes. Lots
of bytes. Things that form a group are not necessarily stored sequentially.

Back to What Is A Python Dictionary: Somebody please enlighten me.


Steve
norseman@hughes .net

[Bruno Desthuilliers]

Re: Multiple values for one key

norseman a écrit :

Terry Reedy wrote:

>>
>>
>Ron Brennan wrote:

>>Hello,
>>>
>>>
>>How would I create a dictionary that contains multiple values for one
>>key.

>>
>Make the value a collection object (set or list if you plan to add and
>delete).
>>

>> I'd also like the key to be able to have duplicate entries.

>>
>Dict keys must be hashable and unique.
>>
>tjr
>>
>--
>http://mail.python.org/mailman/listinfo/python-list
>>

=============== =
First part I understand, second is still giving me a problem.
>
For some reason I still want keys to be dbf column headers.
like:
>
name:address:zi p so forth
---- ------- --- ------------------
guy: unknown:00000
girl: 123 tiny street:12345
boy:321 here:33333
gal:999 over there: 55555
so forth
>
Thus one key has many values. And you can then index on whatever key(s)
you wish - name,zip...

You can either use 1/ a list of dicts, or 2/ a dict mapping keys to lists.

1/
records = [
{"name":"guy ", "address":"unkn own","zip":"000 00"},
{"name":"gir l", "address":" 123 tiny street","zip":" 12345"},
{"name":"boy ", "address":" 321 here","zip":"33 333"},
{"name":"gal ", "address":" 999 over there","zip":"5 5555"},
]

keys = ("name", "address", "zip")

print ":".join(ke ys)
print "-" * len(":".join(ke ys))
for record in records:
data = [record[key] for key in keys]
print ":".join(da ta)


2/
records = dict(
name=["guy", "girl", "boy", "gal"],
address=["unknown"," 123 tiny street","321 there","999 over there"],
zip=["00000", "12345", "33333", "55555"]
)

keys = ("name", "address", "zip")
nb_records = len(records[keys[0]])

print ":".join(ke ys)
print "-" * len(":".join(ke ys))
for i in xrange(nb_recor ds):
data = [data[key][i] for key in keys]
print ":".join(da ta)


You are of course entitled the right to prefer the second solution, but
then I hope I'll never have to maintain your code, since it's obviously
not an appropriate data structure.

With billions plus records,

With billions plus records, it may be time to move to a serious RDBMS.
Which btw will provide solution 1, or a lighter version of it using a
list of tuples, ie:

cursor = connection.curs or()
cursor.execute( "select name, address, zip from peoples")
records = cursor.fetchall ()

# at this time, you have :
#records = [
# ("guy", "unknown","0000 0",),
# ("girl", "123 tiny street","12345" ,),
# ("boy", "321 here","33333",) ,
# ("gal", "999 over there", "55555",),
#]


(snip)

OK - I know I missed the whole concept of a Python Dictionary.

Bad thing for you, since it's the central datastructure in Python.

I haven't
read anything as yet that gives a clear picture of what it is and what
it is for.

Then you failed to read the FineManual's tutorial, which is where you
should have started:

http://docs.python.org/tut/node7.html#SECTION007500000000000000000

Do yourself a favour : read the above first, then if you still have
questions about dicts, we'll gladly try to help.

And do yourself another favour : learn about SQL, relational model and
RDBMS.

(snip description of why the OP *really* wants a RDBMS)

[Tim Rowe]

Re: Multiple values for one key

2008/8/28 Bruno Desthuilliers <bruno.42.desth uilliers@websit eburo.invalid>:

You can either use 1/ a list of dicts, or 2/ a dict mapping keys to lists.
>
1/
records = [
{"name":"guy ", "address":"unkn own","zip":"000 00"},
{"name":"gir l", "address":" 123 tiny street","zip":" 12345"},
{"name":"boy ", "address":" 321 here","zip":"33 333"},
{"name":"gal ", "address":" 999 over there","zip":"5 5555"},
]

I think I'd make a class with members name, address, zip, etc. Then
make a list of instances of that class or (better for access) identify
a primary key -- what *is* unique about each entry -- and use that as
a dictionary key with class instances as values. Or use a DBMS.
Certainly the original poster should read up on database design, or
chances are he'll have a nightmare maintaining referential integrity.

--
Tim Rowe