Reference an Element in a List of Tuples

Question

Sorry in advance  but I m new to Python   I have a list of tuples  and I was wondering how I can reference  say  the first element of each tuple within the list   I would think it s something like   for i in number of tuples     first element   myList i 0     you know   list element tuple element     However  this doesn t appear to be the right approach   Any help would be greatly appreciated   Thanks   Turner

User · Answer

Here s a quick example   termList      termList append   term1    1 2 3 4    termList append   term2    5 6 7 8    termList append   term3    9 10 11 12     result    x 1  for x in termList if x 0      term3    print result

User · Answer

All of the other answers here are correct but do not explain why what you were trying was wrong  When you do myList i 0   you are telling Python that i is a tuple and you want the value or the first element of tuple i as the index for myList   In the majority of programming languages when you need to access a nested data type  such as arrays  lists  or tuples   you append the brackets to get to the innermost item  The first bracket gives you the location of the tuple in your list  The second bracket gives you the location of the item in the tuple   This is a quick rudimentary example that I came up with   info       1  2    3  4    5  6     info 0  0     1 info 0  1     2 info 1  0     3 info 1  1     4 info 2  0     5 info 2  1     6

User · Answer

You also can use itemgetter operator   from operator import itemgetter my tuples      c   r     2  3     e     True  False    text   sample    map itemgetter 0   my tuples

User · Answer

The code  my list     1  2    3  4    5  6   for t in my list      print t   prints   1  2   3  4   5  6    The loop iterates over my list  and assigns the elements of my list to t one after the other   The elements of my list happen to be tuples  so t will always be a tuple   To access the first element of the tuple t  use t 0    for t in my list      print t 0    To access the first element of the tuple at the given index i in the list  you can use  print my list i  0

User · Answer

Rather than   first element   myList i 0     You probably want   first element   myList i  0

User · Answer

You can get a list of the first element in each tuple using a list comprehension    gt  gt  gt  my tuples     1  2  3     a    b    c    d    e     True  False    qwerty    gt  gt  gt  first elts    x 0  for x in my tuples   gt  gt  gt  first elts  1   a   True   q

User · Answer

So you have  a list of tuples   let me assume that you are manipulating some 2-dimension matrix  and  in this case  one convenient interface to accomplish what you need is the one numpy provides   Say you have an array arr   numpy array   1  2    3  4    5  6     you can use arr    0  to get a new array of all the first elements in each  tuple

[python] Reference an Element in a List of Tuples

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