How to merge item in list

Question

I have problem with list in python. When I print "list" I have this results:

[1,2,3]
[4,5,6]

So I have two lists in one variable I guess. How can I merge this items to one variable ?

A variable (or "name" in python), can only be one object at a time. What you have is a list (or similar) containing two lists, containing 1, 2, 3 and 4, 5, 6 respectively. — Benproductions1, Apr 14 '14 at 11:58
possible duplicate of [Merge two lists in Python?](http://stackoverflow.com/questions/1720421/merge-two-lists-in-python) — BlaShadow, Apr 14 '14 at 12:44

score 2 · Answer 1 · answered Apr 14 '14 at 11:57

2

I would do, using itertools.chain:

>>> import itertools
>>> a = [[1, 2, 3], [4 , 5, 6]]
>>> a = itertools.chain.from_iterable(a)
>>> a
[1, 2, 3, 4, 5, 6]

answered Apr 14 '14 at 11:57

anon582847382

19,907
5
54
57

score 0 · Answer 2 · edited Apr 14 '14 at 12:14

0

If:

returnList = [[1,2,3], [4,5,6]]

You can very easily do:

>>> returnList = [j for i in returnList for j in i]

Or:

>>> returnList = [j for i in returnList for j in i]

Alternatively, you can also do:

>>> returnList = reduce(lambda i,j: i+j, returnList)

Both will return: [1, 2, 3, 4, 5, 6]

edited Apr 14 '14 at 12:14

Tejas Pendse

551
6
19

answered Apr 14 '14 at 11:53

sshashank124

31,495
9
67
76

Ok but what I must replace with my variable returnList ? – user3531797 Apr 14 '14 at 12:00
@user3531797, `a` is what you replace – sshashank124 Apr 14 '14 at 12:00

Nishant Nawarkhede · Accepted Answer · 2014-04-14T12:30:44.733

0

Try this ,

>>> a
[[1, 2, 3], [4, 5, 6]]
>>> result=[]
>>> for i in a:
    result+=i


>>> result
[1, 2, 3, 4, 5, 6]
>>>

OR

>>> a
[[1, 2, 3], [4, 5, 6]]
>>> sum(a, [])

Output:

[1, 2, 3, 4, 5, 6]

OR

>>> a1
[1, 2, 3]
>>> a2
[4, 5, 6]
>>> [item for item in itertools.chain(a1, a2)]

Output:

[1, 2, 3, 4, 5, 6]

edited Apr 14 '14 at 12:30

answered Apr 14 '14 at 12:14

Nishant Nawarkhede

8,234
12
59
81

This could be simplified to just `result = sum(a, [])`. – anon582847382 Apr 14 '14 at 12:16
1

Although it is important to note that this is probably rather slow. – anon582847382 Apr 14 '14 at 12:19

heinst · Answer 4 · 2014-04-14T12:33:55.440

0

l = [['0', '1', '2'], ['3', '4', '5']]

def merge_list(l):
    temp = []
    for i in l:
        for j in i:
            temp.append(j)
    return temp

print merge_list(l)

Result

['0', '1', '2', '3', '4', '5']

edited Apr 14 '14 at 12:33

answered Apr 14 '14 at 12:28

heinst

8,520
7
41
77

1

Input and result are same ? – Nishant Nawarkhede Apr 14 '14 at 12:31
1

Yeah didn't even notice...returned input instead of temp...whoops. Thanks for the heads up – heinst Apr 14 '14 at 12:34

score 0 · Answer 5 · edited May 23 '17 at 12:21

0

Merge 2 list in python

listtwo = [8,9,0]
listone = [1,2,3,4,5]
mergedlist = listone + listtwo

edited May 23 '17 at 12:21

Community

1
1

answered Apr 14 '14 at 12:48

BlaShadow

11,075
7
39
60

James Sapam · Answer 6 · 2014-04-14T14:03:24.360

Here I collect some of the solution and just try timeit:

Here is my snippet:

#!/usr/bin/python

def f1(List):
    x = []
    [ x.extend(y) for y in List ]
    return x

def f2(List):
    return sum(List, [])

def f3(List):
    temp = []
    for i in List:
        for j in i:
            temp.append(j)
    return temp

def f4(List):
    result=[]
    for i in List:
        result += i
    return result

def f5(List):
    return [j for i in List for j in i]

import cProfile
import itertools
from faker import Faker
from timeit import Timer

s = Faker()
# instead of faker you can use random module
func = [ f1, f2, f3, f4, f5, f6 ]
Lis = [[ s.random_int(min=1, max=99)
        for x in range(1000) ]
        for x in range(100)]

for fun in func:
    t = Timer(lambda: fun(Lis))
    print fun.__name__, cProfile.run('t.timeit(number=1000)')

Output:

f1          102011 function calls in 0.701 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.701    0.701 <string>:1(<module>)
     1000    0.040    0.000    0.495    0.000 merge.py:3(f1)
     1000    0.001    0.000    0.495    0.000 merge.py:42(<lambda>)
        1    0.000    0.000    0.000    0.000 timeit.py:143(setup)
        1    0.000    0.000    0.701    0.701 timeit.py:178(timeit)
        1    0.206    0.206    0.701    0.701 timeit.py:96(inner)
        1    0.000    0.000    0.000    0.000 {gc.disable}
        1    0.000    0.000    0.000    0.000 {gc.enable}
        1    0.000    0.000    0.000    0.000 {gc.isenabled}
        1    0.000    0.000    0.000    0.000 {globals}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
   100000    0.455    0.000    0.455    0.000 {method 'extend' of 'list' objects}
        2    0.000    0.000    0.000    0.000 {time.time}


None
f2          3011 function calls in 37.747 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000   37.747   37.747 <string>:1(<module>)
     1000    0.003    0.000   37.418    0.037 merge.py:42(<lambda>)
     1000    0.004    0.000   37.415    0.037 merge.py:8(f2)
        1    0.000    0.000    0.000    0.000 timeit.py:143(setup)
        1    0.000    0.000   37.747   37.747 timeit.py:178(timeit)
        1    0.329    0.329   37.747   37.747 timeit.py:96(inner)
        1    0.000    0.000    0.000    0.000 {gc.disable}
        1    0.000    0.000    0.000    0.000 {gc.enable}
        1    0.000    0.000    0.000    0.000 {gc.isenabled}
        1    0.000    0.000    0.000    0.000 {globals}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
     1000   37.411    0.037   37.411    0.037 {sum}
        2    0.000    0.000    0.000    0.000 {time.time}


None
f3          100002011 function calls in 28.044 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000   28.044   28.044 <string>:1(<module>)
     1000   20.304    0.020   27.676    0.028 merge.py:11(f3)
     1000    0.001    0.000   27.677    0.028 merge.py:42(<lambda>)
        1    0.000    0.000    0.000    0.000 timeit.py:143(setup)
        1    0.000    0.000   28.044   28.044 timeit.py:178(timeit)
        1    0.367    0.367   28.044   28.044 timeit.py:96(inner)
        1    0.000    0.000    0.000    0.000 {gc.disable}
        1    0.000    0.000    0.000    0.000 {gc.enable}
        1    0.000    0.000    0.000    0.000 {gc.isenabled}
        1    0.000    0.000    0.000    0.000 {globals}
100000000    7.372    0.000    7.372    0.000 {method 'append' of 'list' objects}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
        2    0.000    0.000    0.000    0.000 {time.time}


None
f4          2011 function calls in 0.826 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.826    0.826 <string>:1(<module>)
     1000    0.463    0.000    0.463    0.000 merge.py:18(f4)
     1000    0.001    0.000    0.464    0.000 merge.py:42(<lambda>)
        1    0.000    0.000    0.000    0.000 timeit.py:143(setup)
        1    0.000    0.000    0.826    0.826 timeit.py:178(timeit)
        1    0.362    0.362    0.826    0.826 timeit.py:96(inner)
        1    0.000    0.000    0.000    0.000 {gc.disable}
        1    0.000    0.000    0.000    0.000 {gc.enable}
        1    0.000    0.000    0.000    0.000 {gc.isenabled}
        1    0.000    0.000    0.000    0.000 {globals}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
        2    0.000    0.000    0.000    0.000 {time.time}


None
f5          2011 function calls in 4.608 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    4.608    4.608 <string>:1(<module>)
     1000    4.253    0.004    4.253    0.004 merge.py:24(f5)
     1000    0.001    0.000    4.254    0.004 merge.py:42(<lambda>)
        1    0.000    0.000    0.000    0.000 timeit.py:143(setup)
        1    0.000    0.000    4.608    4.608 timeit.py:178(timeit)
        1    0.354    0.354    4.608    4.608 timeit.py:96(inner)
        1    0.000    0.000    0.000    0.000 {gc.disable}
        1    0.000    0.000    0.000    0.000 {gc.enable}
        1    0.000    0.000    0.000    0.000 {gc.isenabled}
        1    0.000    0.000    0.000    0.000 {globals}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
        2    0.000    0.000    0.000    0.000 {time.time}


None

How to merge item in list

6 Answers6