[Tutor] Re: Unique Items in Lists

[Wolfram Kraus]

Brian van den Broek wrote:
[...]
Hi Srini,
for the task of finding out which items are repeated and how many times, 
I'd do this:

<code>
def dups_in_list_report(a_list):
    '''Prints a duplication report for a list.'''
    items_dict = {}
    for i in a_list:
        if i in items_dict:
            items_dict[i] = items_dict[i] + 1
        else:
            items_dict[i] = 1
get(key, default) is your friend here:
      for i in a_list:
          items_dict[i] = items_dict.get(i, 0) + 1
get() (and his "brother" setdefault()) are mighty dictionary-methods.
    for key in items_dict.copy():   # Try it without the .copy()
        if items_dict[key] == 1:    # and see what happens.
            del items_dict[key]
    dict_keys = items_dict.keys()
    dict_keys.sort()
>
    for key in dict_keys:
        print '%s occurred %s times' %(key, items_dict[key])
This whole part can be rewritten (without sorting, but in Py2.4 you can 
use sorted() for this) with a list comprehension (Old Python2.1 style, 
with a newer version the keys() aren't needed):
      for k,v in [(k, items_dict[k]) \
      for k in items_dict.keys() if items_dict[k] > 1]:
          print '%s occurred %s times' %(key, items_dict[key])

f = [1,1,2,3,3,3,3,4,4,4,4,4,4,4,5]
dups_in_list_report(f)
</code>
And, now that I get back on-line, I see that Chad posted the same basic 
idea. But, perhaps the extra stuff here is of use, too.
You can apply the get()  there, too ;-)

HTH,
Brian vdB

HTH,
Wolfram
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