How to sort a list tuple of lists tuples by the element at a given index

Question

I have some data either in a list of lists or a list of tuples  like this   data     1 2 3    4 5 6    7 8 9   data     1 2 3    4 5 6    7 8 9     And I want to sort by the 2nd element in the subset  Meaning  sorting by 2 5 8 where 2 is from  1 2 3   5 is from  4 5 6   What is the common way to do this  Should I store tuples or lists in my list

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itemgetter   is somewhat faster than lambda tup  tup 1   but the increase is relatively modest  around 10 to 25 percent     IPython session    gt  gt  gt  from operator import itemgetter  gt  gt  gt  from numpy random import randint  gt  gt  gt  values   randint 0  9  30000  reshape  10000 3    gt  gt  gt  tpls    tuple values i     for i in range len values      gt  gt  gt  tpls  5       display sample from list   1  0  0      8  5  5      5  4  0      5  7  7      4  2  1     gt  gt  gt  sorted tpls  5   key itemgetter 1        example sort   1  0  0      4  2  1      5  4  0      8  5  5      5  7  7     gt  gt  gt   timeit sorted tpls  key itemgetter 1   100 loops  best of 3  4 89 ms per loop   gt  gt  gt   timeit sorted tpls  key lambda tup  tup 1   100 loops  best of 3  6 39 ms per loop   gt  gt  gt   timeit sorted tpls  key  itemgetter 1 0    100 loops  best of 3  16 1 ms per loop   gt  gt  gt   timeit sorted tpls  key lambda tup   tup 1   tup 0    100 loops  best of 3  17 1 ms per loop

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Without lambda   def sec elem s       return s 1   sorted data  key sec elem

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Stephen  s answer is to the point  Here is an example for better visualization   Shout out for the Ready Player One fans       gt  gt  gt  gunters      2044-04-05    parzival      2044-04-07    aech      2044-04-06    art3mis     gt  gt  gt  gunters sort key lambda tup  tup 0    gt  gt  gt  print gunters    2044-04-05    parzival      2044-04-06    art3mis      2044-04-07    aech      key is a function that will be called to transform the collection s items for comparison   like compareTo method in Java    The parameter passed to key must be something that is callable  Here  the use of lambda creates an anonymous function  which is a callable   The syntax of lambda is the word lambda followed by a iterable name then a single block of code    Below example  we are sorting a list of tuple that holds the info abt time of certain event and actor name    We are sorting this list by time of event occurrence - which is the 0th element of a tuple   Note - s sort  cmp   key   reverse      sorts the items of s in place

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Sorting a tuple is quite simple   tuple sorted t

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Stephen s answer is the one I d use   For completeness  here s the DSU  decorate-sort-undecorate  pattern with list comprehensions   decorated     tup 1   tup  for tup in data  decorated sort   undecorated    tup for second  tup in decorated    Or  more tersely    b for a b in sorted  tup 1   tup  for tup in data     As noted in the Python Sorting HowTo  this has been unnecessary since Python 2 4  when key functions became available

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sorted by second   sorted data  key lambda tup  tup 1     or   data sort key lambda tup  tup 1      sorts in place

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I just want to add to Stephen s answer if you want to sort the array from high to low  another way other than in the comments above is just to add this to the line    reverse   True   and the result will be as follows   data sort key lambda tup  tup 1   reverse True

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from operator import itemgetter data sort key itemgetter 1

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In order to sort a list of tuples   lt word gt    lt count gt    for count in descending order and word in alphabetical order   data       betty   1     bought   1     a   1     bit   1     of   1     butter   2     but   1     the   1     was   1     bitter   1     I use this method   sorted data  key lambda tup  -tup 1   tup 0      and it gives me the result      butter   2     a   1     betty   1     bit   1     bitter   1     bought   1     but   1     of   1     the   1     was   1

User · Answer

For sorting by multiple criteria  namely for instance by the second and third elements in a tuple  let  data     1 2 3   1 2 1   1 1 4     and so define a lambda that returns a tuple that describes priority  for instance  sorted data  key lambda tup   tup 1  tup 2       1  1  4    1  2  1    1  2  3

[python] How to sort a list/tuple of lists/tuples by the element at a given index?

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