How to search a list of tuples in Python

Question

So I have a list of tuples such as this     1  juca    22  james    53  xuxa    44  delicia      I want this list for a tuple whose number value is equal to something   So that if I do search 53  it will return the index value of 2  Is there an easy way to do this

User · Answer

Hmm    well  the simple way that comes to mind is to convert it to a dict  d   dict thelist    and access d 53    EDIT  Oops  misread your question the first time  It sounds like you actually want to get the index where a given number is stored  In that case  try  dict  t 0   i  for i  t in enumerate thelist     instead of a plain old dict conversion  Then d 53  would be 2

User · Answer

You can use a list comprehension    gt  gt  gt  a     1  juca    22  james    53  xuxa    44  delicia     gt  gt  gt   x 0  for x in a   1  22  53  44   gt  gt  gt   x 0  for x in a  index 53  2

User · Answer

Just another way   zip  a  0  index 53

User · Answer

k for k v in l if v    delicia    here l is the list of tuples-  1  juca    22  james    53  xuxa    44  delicia     And instead of converting it to a dict  we are using llist comprehension    Key  in Key Value in list  where value     delicia

User · Answer

tl dr  A generator expression is probably the most performant and simple solution to your problem     l     1  juca    22  james    53  xuxa    44  delicia     result   next  i for i  v in enumerate l  if v 0     53   None    2   Explanation  There are several answers that provide a simple solution to this question with list comprehensions  While these answers are perfectly correct  they are not optimal  Depending on your use case  there may be significant benefits to making a few simple modifications   The main problem I see with using a list comprehension for this use case is that the entire list will be processed  although you only want to find 1 element   Python provides a simple construct which is ideal here  It is called the generator expression  Here is an example     Our input list  same as before l     1  juca    22  james    53  xuxa    44  delicia       Call next on our generator expression  next  i for i  v in enumerate l  if v 0     53   None    We can expect this method to perform basically the same as list comprehensions in our trivial example  but what if we re working with a larger data set  That s where the advantage of using the generator method comes into play  Rather than constructing a new list  we ll use your existing list as our iterable  and use next   to get the first item from our generator   Lets look at how these methods perform differently on some larger data sets  These are large lists  made of 10000000   1 elements  with our target at the beginning  best  or end  worst   We can verify that both of these lists will perform equally using the following list comprehension   List comprehensions   Worst case   worst case      False   F      10000000      True   T    print  i for i  v in enumerate worst case  if v 0  is True      10000000             2 function calls in 3 885 seconds        Ordered by  standard name        ncalls  tottime  percall  cumtime  percall filename lineno function            1    3 885    3 885    3 885    3 885 so lc py 1  lt module gt             1    0 000    0 000    0 000    0 000  method  disable  of   lsprof Profiler  objects     Best case   best case     True   T         False   F      10000000  print  i for i  v in enumerate best case  if v 0  is True      0             2 function calls in 3 864 seconds        Ordered by  standard name        ncalls  tottime  percall  cumtime  percall filename lineno function            1    3 864    3 864    3 864    3 864 so lc py 1  lt module gt             1    0 000    0 000    0 000    0 000  method  disable  of   lsprof Profiler  objects    Generator expressions  Here s my hypothesis for generators  we ll see that generators will significantly perform better in the best case  but similarly in the worst case  This performance gain is mostly due to the fact that the generator is evaluated lazily  meaning it will only compute what is required to yield a value   Worst case    10000000            5 function calls in 1 733 seconds        Ordered by  standard name        ncalls  tottime  percall  cumtime  percall filename lineno function            2    1 455    0 727    1 455    0 727 so lc py 10  lt genexpr gt             1    0 278    0 278    1 733    1 733 so lc py 9  lt module gt             1    0 000    0 000    0 000    0 000  method  disable  of   lsprof Profiler  objects            1    0 000    0 000    1 455    1 455  next    Best case  best case      True   T         False   F      10000000  print next  i for i  v in enumerate best case  if v 0     True   None     0            5 function calls in 0 316 seconds        Ordered by  standard name        ncalls  tottime  percall  cumtime  percall filename lineno function            1    0 316    0 316    0 316    0 316 so lc py 6  lt module gt             2    0 000    0 000    0 000    0 000 so lc py 7  lt genexpr gt             1    0 000    0 000    0 000    0 000  method  disable  of   lsprof Profiler  objects            1    0 000    0 000    0 000    0 000  next    WHAT   The best case blows away the list comprehensions  but I wasn t expecting the our worst case to outperform the list comprehensions to such an extent  How is that  Frankly  I could only speculate without further research   Take all of this with a grain of salt  I have not run any robust profiling here  just some very basic testing  This should be sufficient to appreciate that a generator expression is more performant for this type of list searching   Note that this is all basic  built-in python  We don t need to import anything or use any libraries   I first saw this technique for searching in the Udacity cs212 course with Peter Norvig

User · Answer

Your tuples are basically key-value pairs--a python dict--so   l     1  juca    22  james    53  xuxa    44  delicia    val   dict l  53    Edit -- aha  you say you want the index value of  53   xuxa    If this is really what you want  you ll have to iterate through the original list  or perhaps make a more complicated dictionary   d   dict  n i  for  i n  in enumerate e 0  for e in l   idx   d 53

User · Answer

Supposing the list may be long and the numbers may repeat  consider using the SortedList type from the Python sortedcontainers module  The SortedList type will automatically maintain the tuples in order by number and allow for fast searching   For example   from sortedcontainers import SortedList sl   SortedList   1  juca    22  james    53  xuxa    44  delicia        Get the index of 53   index   sl bisect  53       With the index  get the tuple   tup   sl index    This will work a lot faster than the list comprehension suggestion by doing a binary search  The dictionary suggestion will be faster still but won t work if there could be duplicate numbers with different strings   If there are duplicate numbers with different strings then you need to take one more step   end   sl bisect  53   1     results   sl index end    By bisecting for 54  we will find the end index for our slice  This will be significantly faster on long lists as compared with the accepted answer

User · Answer

i for i  v in enumerate L  if v 0     53

[python] How to search a list of tuples in Python

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