On Wed, 26 Jan 2005, Srinivas Iyyer wrote:
> I have a list with 4 columns and column1 elements are unique. I wanted > to extract unique elements in column3 and and place the other elements > of the column along with unique elements in column 4 as a tab delim > text. > > Table: > > col1 col2 col3 col4 > A Apple 5 Chennai > B Baby 11 Delhi > I Baby* 1 Delhi > M Dasheri+ 5 Mumbai > K Apple 12 Copenhagen [Meta: we seem to be getting a run of similar questions this week. Scott Melnyk also asked about grouping similar records together: http://mail.python.org/pipermail/tutor/2005-January/035185.html.] Hi Srinivas, I see that you are trying to group records based on some criterion. You may find the problem easier to do if you fist do a sort on that criterion column: that will make related records "clump" together. For your sample data above, if we sort against the second column, the records will end up in the following order: ### A Apple 5 Chennai K Apple 12 Copenhagen B Baby 11 Delhi I Baby 1 Delhi M Dasheri 5 Mumbai ### In this sorting approach, you can then run through the sorted list in order. Since all the related elements should be adjacent, grouping related lines together should be much easier, and you should be able to produce the final output: ### Apple A,K 5,12 Chennai,Copenhagen Baby B,I 1,11 Delhi Dasheri M 5 Mumbai ### without too much trouble. You can do this problem without dictionaries at all, although you may find the dictionary approach a little easier to implement. > A dictionary option does not work A dictionary approach is also very possible. The thing you may be stuck on is trying to make a key associate with multiple values. Most examples of dictionaries in tutorials use strings as both the keys and values, but dictionaries are more versatile: we can also make a dictionary whose values are lists. For example, here is a small program that groups words by their first letters: ### >>> def groupAlpha(words): ... groups = {} ... for w in words: ... firstLetter = w[0] ... if firstLetter not in groups: ... groups[firstLetter] = [] ... groups[firstLetter].append(w) ... return groups ... >>> groupAlpha("this is a test of the emergency broadcast system".split()) {'a': ['a'], 'b': ['broadcast'], 'e': ['emergency'], 'i': ['is'], 'o': ['of'], 's': ['system'], 't': ['this', 'test', 'the']} ### If you have more questions, please feel free to ask. _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
