fetching certain elements in a list in python

Question

I am new to Python. Imagine we have a list like this: [(1,0.2), (2,4.8), (5,5.6)] I want to fetch the all left side elements so that I have a list like this: [1,2,5] I am wondering how I can do that. Thanks

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score 3 · Accepted Answer · answered Nov 09 '15 at 15:50

3

You can use a list comprehension statement like:

example = [(1,0.2), (2,4.8), (5,5.6)]
[x[0] for x in example]

which basically iterates through all your elements, and grabs the first element in each tuple, and creates a new array out of it.

answered Nov 09 '15 at 15:50

ergonaut

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score 2 · Answer 2 · answered Nov 09 '15 at 15:51

m =  [(1,0.2), (2,4.8), (5,5.6)] 

out_list = []
for element in m:
    out_list.append(element[0])
print out_list

You have to navigate thru all the elements of m , then, take the first number with element[0] and append it to a new list titled out_list

The code will output

[1,2,5]

You can you this on a more ellegant way using list comprehension as follows:

out_list = [element[0] for element in m ] 
print out_list

score 0 · Answer 3 · edited May 23 '17 at 11:59

Most people suggest list comprehension as the solution to your problem, which is great. But python can do the same thing via different approaches. Recently I learnt how to "unzip" a list and the technique fits right into your problem.

zipped = [(1,0.2), (2,4.8), (5,5.6)]
list(zip(*zipped)[0])

In this thread, people explained how it works. Hope you will get something from it. Welcome to the python world!

fetching certain elements in a list in python

3 Answers3