efficient matching of elements a list

[omission9]

Suppose I have a lists of tuples
A_LIST=[(1,6,7),(7,4,2),(7,9,2),(1,5,5),(1,1,1)]
and an int
i=1
What is the fastest way in python to get out all the tuples from the
list whose first element is equal to i?
A have a very large list and a simple
for a in A_LIST:
if a[0]==i:
#We have a match!!

Seems to be very slow and there must be some super quick pythonic way to
do this maybe?
Any avice would be much appreciated!!

 

[Paul Rubin]

Suppose I have a lists of tuples
A_LIST=[(1,6,7),(7,4,2),(7,9,2),(1,5,5),(1,1,1)]
and an int
i=1
What is the fastest way in python to get out all the tuples from the
list whose first element is equal to i?

t = [x for x in A_LIST if x[0] == i]

Seems to be very slow and there must be some super quick pythonic way
to do this maybe?
Any avice would be much appreciated!!

Maybe there's some obscure faster way to do it but if you're really
in a hurry, use psyco or pyrex or write a C extension.

 

[Josiah Carlson]

Suppose I have a lists of tuples

A_LIST=[(1,6,7),(7,4,2),(7,9,2),(1,5,5),(1,1,1)]
and an int
i=1
What is the fastest way in python to get out all the tuples from the
list whose first element is equal to i?

t = [x for x in A_LIST if x[0] == i]

Before list comprehensions, we had to do it all with filter...
t = filter(lambda x:x[0]==i, A_LIST)

List comprehension seem to be around 33% faster. Long live list
comprehensions.

- Josiah

 

[Gerrit Holl]

What is the fastest way in python to get out all the tuples from the

list whose first element is equal to i?

Use a list comprehension:

L = [(1,2,3), (2,3,1), (3,2,1), (1,2,5), (5,1,3)]
[t for t in L if t[0] == 1]

[(1, 2, 3), (1, 2, 5)]

yours,
Gerrit.

 

[Rene Pijlman]

omission9:

Suppose I have a lists of tuples
What is the fastest way in python to get out all the tuples from the
list whose first element is equal to i?

A list is not an efficient data structure for this query. Why don't you
design another data structure?