CODEWITHSUNDEEP
pythonlisttuplesmax
R_J
R_J

Reputation: 77

How to extract the n-th elements equal to a value from a list of tuples in python

I'm trying to obtain the nth elements from a list of tuples in python equal to a certain value

I have a much larger list of something like this

num = [('A15', 2, 'BC', 721.16), ('A21', 3, 'AB', 631.31), ('A42', 4, 'EE', 245.43)]

I wish to extract only the tuples with the 2nd element of the tuple equal to a given value i.e. 2 in this example and from those find the largest 4th element

Currently my code looks like the following

for ((x[1] for x in num) = 1):
    num_max = max(num_list,key=lambda item:item[3])

the problem's something to do with setting the list comprehension equal to a value as that's what's giving me a syntax error

Apologies if this has already been answered but I couldn't find it

Upvotes: 2

Views: 127

Answers (2)

Rahul K P
Rahul K P

Reputation: 16091

Try like this,

In [1]: num = [('A15', 2, 'BC', 721.16), ('A21', 3, 'AB', 631.31), 
               ('A42', 4, 'EE', 245.43),('A15', 2, 'BC', 856.16)]
In [2]: max((i for i in num if i[1] == 2),key=lambda  x:x[3])
Out[2]: ('A15', 2, 'BC', 856.16)

Upvotes: 1

Netwave
Netwave

Reputation: 42746

You have several options, using filter and max for example:

result =  max(filter(lambda x: x[1] == 2, num_list), key=lambda x: x[3])

As commented by @chrisz, but instead of a list use a generator:

result = max((i for i in x if i[1] == 2), key=lambda x: x[3])

Note: If using python2 consider using itertools.ifilter instead of filter to avoid extra memory.

Upvotes: 0

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