[Tutor] Mapping ID's for corresponding values in different Columns

[Fred G]

Got it! Thanks guys for all your help--what a satisfying feeling!  Just out
of curiosity, in the following:

def new_dict (csv_to_dict, nested_line):
    old_dict = csv_to_dict(file1)
    old_list = nested_line(file2)
    new_dict = {}
    #for item in old_list:
    #    new_dict[item] = item
    for k, v in old_dict.iteritems():
        for item in old_list:
            if k == item:
                new_dict[item] = v
    return (new_dict)

when I deleted the third line from the bottom (the "if k == item"), I got
the same value ("3") for each key, instead of the correct output (ie the
different ID's).  Does anyone know why this was the case?

Thanks so much.


On Mon, Jul 9, 2012 at 8:23 AM, Fred G <bayespokerguy at gmail.com> wrote:

> Thank you guys so much.  I'm quite close now, but I'm having a bit of
> trouble on the final for-loop to create the new dictionary.  I have the
> following 3 functions (note I'm re-typing it from a different computer so
> while the identation will be off here, it is correct in the actual code):
>
> #read in file as dictionary.  Name is key, id is value.
> def csv_to_dict(filename):
>   record = {}
>   line = filename.readline()
>   for line in filename:
>     key = line.split(",", 1)[-1]
>     val = line.split(",", 1)[:-1]
>   return record
>
> #read in file2 names
> def nested_line(filename):
>   line = filename.readline()
>   new_list = []
>   for line in filename:
>     name = line.split(",", 1)[-1]
>     new_list.append(name)
>   return new_list
>
> #this is the function that I'm having trouble with
> #create new dict mapping file 1 ids to file2's names
> def new_dict (csv_to_dict, nested_line):
>   old_dict = cssv_to_dict(file1)
>   old_list = nested_line(file2)
>   new_dict1 = {}
>   for item in old_list:
>     new_dict1[item] = item
>   return (new_dict1)
>
> I have tried various permutations of the for loop in this final function,
> but I haven't quite gotten it.  The current form is the closest I have
> gotten to my desired output, since it produces the new dictionary with the
> name that I want-- just an invalid id associated with that name.  I tried a
> bunch of different nested loops but kept getting it incorrect and then
> after so many attempts I got a little confused about what I was trying to
> do.  So I backed up a little bit and have this.
>
> Conceptually, I thought that this would give me my desired result:
> new_dict
> for name in old_list:
>   for key, value in old_dict:
>     if name == key:
>       new_dict1[key] = value
> return(new_dict1)
>
> But it wasn't right.  I tried a different approach where I used the
> dict.values() function in order to pull out the values from old_dict that
> we want to include in the new_dict, but I got a bit lost there, too.
>
> I'm so close right now and I would be so thankful for any bit of
> clarification which could get me to the finish line.
>
> On Mon, Jul 9, 2012 at 12:42 AM, Hugo Arts <hugo.yoshi at gmail.com> wrote:
>
>> On Sun, Jul 8, 2012 at 11:47 PM, Fred G <bayespokerguy at gmail.com> wrote:
>>
>>> Hi--
>>>
>>> My current input looks like the following:
>>>
>>> FILE1.csv
>>> PERSON_ID    PERSON_NAME
>>> 1                     Jen
>>> 2                     Mike
>>> 3                     Jim
>>> 4
>>> 5                     Jane
>>> 6                     Joe
>>> 7                     Jake
>>>
>>> FILE2.csv
>>> PERSON_ID   PERSON_NAME
>>>                      Jim
>>>                      Mike
>>>                      Jane
>>>                      Todd
>>>                      Jen
>>>
>>> _________
>>> I want to fill into the PERSON_ID column of FILE2.csv the corresponding
>>> ID's associated with those names as identified in FILE1.csv.
>>>
>>> At first I imported the csv module and was using the csv.Reader, but
>>> then it seemed simple enough just to write something like:
>>> for line in file2:
>>>      print(line)
>>>
>>> giving me the following output:
>>> PERSON_ID, PERSON_NAME
>>> , Jim
>>> , Mike
>>> , Jane
>>> , Todd
>>> , Jen
>>>
>>> I think I understand the issue at a conceptual level, but not quite sure
>>> how to fully implement it:
>>> a) I want to build a dictionary to create keys, such that each number in
>>> file1 corresponds to a unique string in column B of file1.
>>> b) then write a for loop like the following:
>>> for "person_name" in file2:
>>>    if "person_name.file2" == "person_name.file1":
>>>        person_id.file2 == person_id.file1
>>> c) write into file2 the changes to person_id's...
>>>
>>> But it's pretty difficult for me to get past this stage. Am I on the
>>> right track? And more importantly, how could I learn how to actually
>>> implement this in smaller stages?
>>>
>>>
>>  You're on the right track, and you're almost there! You've already
>> broken down the problem into steps. You should now try to implement a
>> function for each step, and finally you should glue these functions
>> together into a final program.
>>
>> a) Though you don't *have* to use it, csv.reader is really quite simple,
>> I'd recommend it. Try and write a function that takes a file name as
>> argument and returns a dictionary of the form { name: id, name: id } (i.e.
>> the names are the keys).
>>
>> b) For this step, you first need a list of all names in file 2. You could
>> use csv.reader again or you could just parse it. Then, you use the
>> dictionary to look up the corresponding id. The end goal for this function
>> is to return a list of lists that looks much like the file you want to end
>> up with:
>>
>> [[id, name],
>>  [id, name],
>>  [id, name]]
>>
>> c) this step should now be easy. I'd again, recommend csv.writer, it
>> makes the process pretty simple. You just pass in the nested list from step
>> (b) and you're pretty much done.
>>
>> For tips on the csv module, the list of examples is pretty helpful:
>> http://docs.python.org/py3k/library/csv.html#examples
>>  If you need help constructing the lists and dictionaries, my tips would
>> be 1) think one row at a time, 2) the for loop is your best friend, and 3)
>> nested lists usually means nested loops
>>
>> HTH,
>> Hugo
>>
>
>
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