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Dec 29th, 2006

list in another list

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is there an easy way to detect if the entire contents of one list are in another?

if I have a list like this: li = [1,2]
and I have another which will have random values, I want the program to do something only if every value of li is in the second list.

I need a way to program this:

Python Syntax (Toggle Plain Text)
x = random.randint(0,10)
y = random.randint(0,10)
li = [1,2]
li2 = [x,y]
 
 
if every value of li2 is in li:
    do this
x = random.randint(0,10)
y = random.randint(0,10)
li = [1,2]
li2 = [x,y]


if every value of li2 is in li:
    do this

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Matt Tacular

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since Jun 2006

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Dec 29th, 2006

Re: list in another list

Hi!

I don't know if you would call this easy, but it seems to work:

Python Syntax (Toggle Plain Text)
def is_sublist( lst1, lst2 ):
     for elem in lst1:
         if elem not in lst2:
             return False
     return True
def is_sublist( lst1, lst2 ):
     for elem in lst1:
         if elem not in lst2:
             return False
     return True

e.g.:

Python Syntax (Toggle Plain Text)
l1 = [1,2]
l2 = [2,4,6]
l3 = [1,2,3]
print is_sublist(l1, l2)   # --> False
print is_sublist(l1, l3)   # --> True
l1 = [1,2]
l2 = [2,4,6]
l3 = [1,2,3]
print is_sublist(l1, l2)   # --> False
print is_sublist(l1, l3)   # --> True

If you use sets instead of lists, there is a builtin function:

Python Syntax (Toggle Plain Text)
s1 = set([1,2])
s2 = set([2,3,4])
s3 = set([1,2,3])
print s1.issubset(s2)
print s2.issubset(s3)
s1 = set([1,2])
s2 = set([2,3,4])
s3 = set([1,2,3])
print s1.issubset(s2)
print s2.issubset(s3)

Hope this helps.

Regards, mawe

mawe

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since Sep 2005

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Dec 29th, 2006

Re: list in another list

You can use type()

Python Syntax (Toggle Plain Text)
x = random.randint(0,10)
y = random.randint(0,10)
li = [1,2]
li2 = [x,y]
 
test_list = []
if every_value of li2 is in li:
    if type(every_value) == type(test_list) :
       do this
x = random.randint(0,10)
y = random.randint(0,10)
li = [1,2]
li2 = [x,y]

test_list = []
if every_value of li2 is in li:
    if type(every_value) == type(test_list) :
       do this

Note that 'of li2 is in li' will compare entire list to list, not each element, assuming every_value is a list. It is not considered good code practice to use the letters 'el', 'eye', or 'oh' for variable names as they look too much like numbers and are confusing.

woooee

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Solved Threads: 694

Nearly a Posting Maven

Online

2,314 posts
since Dec 2006

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Dec 29th, 2006

Re: list in another list

Click to Expand / Collapse Quote originally posted by Matt Tacular ...

is there an easy way to detect if the entire contents of one list are in another?

if I have a list like this: li = [1,2]
and I have another which will have random values, I want the program to do something only if every value of li is in the second list.

I need a way to program this:
Python Syntax (Toggle Plain Text)
x = random.randint(0,10)
y = random.randint(0,10)
li = [1,2]
li2 = [x,y]
 
 
if every value of li2 is in li:
    do this
x = random.randint(0,10) y = random.randint(0,10) li = [1,2] li2 = [x,y] if every value of li2 is in li: do this

if your lists comparing only numbers, you can sort them first?

Python Syntax (Toggle Plain Text)
if sorted(li) == sorted(li2):
   do something
if sorted(li) == sorted(li2):
   do something

ghostdog74

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156 posts
since Apr 2006

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Dec 30th, 2006

Re: list in another list

This will not work because list a and b are not the same length ...
[php]a = [1, 2]
b = [2, 3, 6, 1]
# this will not work here ...
if sorted(a) == sorted(b):
print 'a is in b'
else:
print 'a is not in b'
[/php]
Using set() will work, like mawe said ...
[php]a = [1, 2]
b = [2, 3, 6, 1]
# this will work ...
if set(a).issubset(set(b)):
print 'a is in b'
else:
print 'a is not in b'
[/php]The next approach is pretty universal ...
[php]def is_a_in_b(a, b):
"""returns True if all elements in list a are in list b, else False"""
ax = []
for x in a:
for y in b:
if x == y:
ax.append(y)
return a == ax

print is_a_in_b([1, 2], [2, 3, 6, 1]) # True
print is_a_in_b([1, 2], [1, 3, 7, 9, 4]) # False
[/php]

vegaseat

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DaniWeb's Hypocrite

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