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Nested List Searches

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Nested List Searches

 
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  #1
Jan 8th, 2007
I was experimenting with the nested list example in thread:
http://www.daniweb.com/techtalkforum...246791-72.html
and was trying to search a nested list like that:
Python Syntax (Toggle Plain Text) 
  1. nested_list = [1 ,'Dick', 2, ['Mary', 7, 9, [700, 777, 'Paul']], 13]
  2.  
  3. if 'Paul' in nested_list:
  4.     print 'found Paul'
  5. else:
  6.     print 'Paul not found'
It always tells me that 'Paul' is not found! How come? Is there an error in Python?
No one died when Clinton lied.
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Re: Nested List Searches

 
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  #2
Jan 9th, 2007
if you just want to find "Paul" in your example, one way to do it is to convert that list to string
Python Syntax (Toggle Plain Text) 
  1. astring  = ','.join( str(i) for i in nested_list)
  2. if "Paul in astring:
  3.   print "Found"
  4.  
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Re: Nested List Searches

 
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  #3
Jan 9th, 2007
Python Syntax (Toggle Plain Text) 
  1. if "x" in nested
can be written as
Python Syntax (Toggle Plain Text) 
  1. for elem in nested: if elem == "x" ...
Your list nested_list = [1 ,'Dick', 2, ['Mary', 7, 9, [700, 777, 'Paul']], 13] consists of 5 elemenst:
1
'Dick'
2
['Mary', 7, 9, [700, 777, 'Paul']]
13

As you can see, none of these passes the test "Paul" == elem. In the 4th one (['Mary', 7, 9, [700, 777, 'Paul']]) there is the string Paul, but it is hidden in a list
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Re: Nested List Searches

 
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  #4
Jan 9th, 2007
You can flatten the list, might call this un-nesting and then search ...
python Syntax (Toggle Plain Text) 
  1. def xflatten(seq):
  2.     """a generator to flatten a nested list"""
  3.     for x in seq:
  4.         if type(x) is list:
  5.             for y in xflatten(x):
  6.                 yield y
  7.         else:
  8.             yield x
  9. nested_list = [1 ,'Dick', 2, ['Mary', 7, 9, [700, 777, 'Paul']], 13]
  10. flat_list = list(xflatten(nested_list))
  11. print flat_list  # [1, 'Dick', 2, 'Mary', 7, 9, 700, 777, 'Paul', 13]
  12. if 'Paul' in flat_list:
  13.     print "Found Paul in flat_list"  # now it works!
If you are only searching, Ghostdog's solution is most elegant and can be simplified to ...
python Syntax (Toggle Plain Text) 
  1. nested_list = [1 ,'Dick', 2, ['Mary', 7, 9, [700, 777, 'Paul']], 13]
  2. nl_string = str(nested_list)
  3. print nl_string  # "[1, 'Dick', 2, ['Mary', 7, 9, [700, 777, 'Paul']], 13]"
  4. if 'Paul' in nl_string:
  5.     print "Found Paul in the string"  # works too!
May 'the Google' be with you!
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Re: Nested List Searches

 
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  #5
Jan 9th, 2007
Thank you fellow Pythonians. I learned from mawe's explanation that in order to find an item or find the maximum item you have to un-nest the list as shown by vegaseat's code.

Converting the list to a string, as Ghostdog74 suggested, works well for the search, but can't find the maximum.
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Re: Nested List Searches

 
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  #6
Jan 9th, 2007
Sneekula,
since you are so refreshingly inquisitive, have you tried this ...
python Syntax (Toggle Plain Text) 
  1. flat_list = [1, 'Dick', 2, 'Mary', 7, 9, 700, 777, 'Paul', 13]
  2. print max(flat_list)
Would you have predicted the outcome? Can you explain why?
May 'the Google' be with you!
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