sets and subsets

**Amy G** · Jul 18 '05, 08:22 AM

Re: sets and subsets

I am sure there is a much more elegant way to do this, but here is one
solution.

for item in c:
if b.count(item) > 0:
b.remove(item)

"Bart Nessux" <bart_nessux@ho tmail.com> wrote in message
news:c0e4g3$r1$ 1@solaris.cc.vt .edu...[color=blue]
> By using lists, I can create sets of number. Suppose I have three lists.
> One list is the super-set, one is a set that contains all the numbers
> (just like the super-set) and the last is sub-set of the super-set. For
> example:
>
> a = [1,2,3,4,5] # The super-set.
> b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
> c = [2,4] # A sub-set
>
> I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
> this would make the sets look like this:
>
> a = [1,2,3,4,5]
> b = [1,3,5]
> c = [2,4]
>
> How do I test set c to find what it contains and then look at set b to
> see if it contains any of those same numbers, and if so, remove them.
>[/color]

**Elaine Jackson** · Jul 18 '05, 08:22 AM

Re: sets and subsets

b=[x for x in b if x not in c]

"Bart Nessux" <bart_nessux@ho tmail.com> wrote in message
news:c0e4g3$r1$ 1@solaris.cc.vt .edu...
| By using lists, I can create sets of number. Suppose I have three lists.
| One list is the super-set, one is a set that contains all the numbers
| (just like the super-set) and the last is sub-set of the super-set. For
| example:
|
| a = [1,2,3,4,5] # The super-set.
| b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
| c = [2,4] # A sub-set
|
| I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
| this would make the sets look like this:
|
| a = [1,2,3,4,5]
| b = [1,3,5]
| c = [2,4]
|
| How do I test set c to find what it contains and then look at set b to
| see if it contains any of those same numbers, and if so, remove them.
|

**Amy G** · Jul 18 '05, 08:22 AM

Re: sets and subsets

There you go... list comprehension. That is definatly nicer to look at.

"Elaine Jackson" <elainejackson7 355@home.com> wrote in message
news:zcxWb.4640 65$JQ1.270296@p d7tw1no...[color=blue]
> b=[x for x in b if x not in c]
>
> "Bart Nessux" <bart_nessux@ho tmail.com> wrote in message
> news:c0e4g3$r1$ 1@solaris.cc.vt .edu...
> | By using lists, I can create sets of number. Suppose I have three lists.
> | One list is the super-set, one is a set that contains all the numbers
> | (just like the super-set) and the last is sub-set of the super-set. For
> | example:
> |
> | a = [1,2,3,4,5] # The super-set.
> | b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
> | c = [2,4] # A sub-set
> |
> | I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
> | this would make the sets look like this:
> |
> | a = [1,2,3,4,5]
> | b = [1,3,5]
> | c = [2,4]
> |
> | How do I test set c to find what it contains and then look at set b to
> | see if it contains any of those same numbers, and if so, remove them.
> |
>
>[/color]

**Lee Harr** · Jul 18 '05, 08:22 AM

Re: sets and subsets

On 2004-02-11, Bart Nessux <bart_nessux@ho tmail.com> wrote:[color=blue]
> By using lists, I can create sets of number. Suppose I have three lists.
> One list is the super-set, one is a set that contains all the numbers
> (just like the super-set) and the last is sub-set of the super-set. For
> example:
>
> a = [1,2,3,4,5] # The super-set.
> b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
> c = [2,4] # A sub-set
>
> I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
> this would make the sets look like this:
>
> a = [1,2,3,4,5]
> b = [1,3,5]
> c = [2,4]
>
> How do I test set c to find what it contains and then look at set b to
> see if it contains any of those same numbers, and if so, remove them.
>[/color]

[color=blue][color=green][color=darkred]
>>> from sets import Set
>>> a = Set([1, 2, 3, 4, 5])
>>> b = Set([1, 2, 3, 4, 5])
>>> c = Set([2, 4])
>>> s = b - c
>>> s[/color][/color][/color]
Set([1, 3, 5])

**Bart Nessux** · Jul 18 '05, 08:22 AM

Re: sets and subsets

Works great too. Thanks to all for the info.

Amy G wrote:[color=blue]
> There you go... list comprehension. That is definatly nicer to look at.
>
>
> "Elaine Jackson" <elainejackson7 355@home.com> wrote in message
> news:zcxWb.4640 65$JQ1.270296@p d7tw1no...
>[color=green]
>>b=[x for x in b if x not in c]
>>
>>"Bart Nessux" <bart_nessux@ho tmail.com> wrote in message
>>news:c0e4g3$r 1$1@solaris.cc. vt.edu...
>>| By using lists, I can create sets of number. Suppose I have three lists.
>>| One list is the super-set, one is a set that contains all the numbers
>>| (just like the super-set) and the last is sub-set of the super-set. For
>>| example:
>>|
>>| a = [1,2,3,4,5] # The super-set.
>>| b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
>>| c = [2,4] # A sub-set
>>|
>>| I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
>>| this would make the sets look like this:
>>|
>>| a = [1,2,3,4,5]
>>| b = [1,3,5]
>>| c = [2,4]
>>|
>>| How do I test set c to find what it contains and then look at set b to
>>| see if it contains any of those same numbers, and if so, remove them.
>>|
>>
>>[/color]
>
>
>[/color]

**Peter Otten** · Jul 18 '05, 08:22 AM

Re: sets and subsets

Bart Nessux wrote:
[color=blue]
> By using lists, I can create sets of number. Suppose I have three lists.
> One list is the super-set, one is a set that contains all the numbers
> (just like the super-set) and the last is sub-set of the super-set. For
> example:
>
> a = [1,2,3,4,5] # The super-set.
> b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
> c = [2,4] # A sub-set
>
> I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
> this would make the sets look like this:
>
> a = [1,2,3,4,5]
> b = [1,3,5]
> c = [2,4]
>
> How do I test set c to find what it contains and then look at set b to
> see if it contains any of those same numbers, and if so, remove them.[/color]

You want set operations, so why would you use lists?
[color=blue][color=green][color=darkred]
>>> from sets import Set
>>> a = Set([1,2,3,4,5])
>>> c = Set([2,4])
>>> b = a - c
>>> b[/color][/color][/color]
Set([1, 3, 5])

Peter

**Bart Nessux** · Jul 18 '05, 08:22 AM

Re: sets and subsets

Peter Otten wrote:[color=blue]
> Bart Nessux wrote:
>
>[color=green]
>>By using lists, I can create sets of number. Suppose I have three lists.
>>One list is the super-set, one is a set that contains all the numbers
>>(just like the super-set) and the last is sub-set of the super-set. For
>>example:
>>
>>a = [1,2,3,4,5] # The super-set.
>>b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
>>c = [2,4] # A sub-set
>>
>>I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
>>this would make the sets look like this:
>>
>>a = [1,2,3,4,5]
>>b = [1,3,5]
>>c = [2,4]
>>
>>How do I test set c to find what it contains and then look at set b to
>>see if it contains any of those same numbers, and if so, remove them.[/color]
>
>
> You want set operations, so why would you use lists?[/color]

All my data are in lists:

inputFile = file('ips.txt', 'r') #Super-set
include = inputFile.readl ines()
inputFile.close ()

# The file below is compiled manually by hand... add IPs to it
# whenever you want to exclude them from IP_protection.
readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
exclude = readFile.readli nes()
readFile.close( )

include = [x for x in include if x not in exclude] #Magic of Elaine

outputFile = file('pruned_ip s.txt' , 'w')
for i in include:
print>> outputFile, i,
outputFile.clos e()

**Aahz** · Jul 18 '05, 08:22 AM

Re: sets and subsets

[content at *bottom*]

In article <c0e890$6hu$1@s olaris.cc.vt.ed u>,
Bart Nessux <bart_nessux@ho tmail.com> wrote:[color=blue]
>Works great too. Thanks to all for the info.
>
>Amy G wrote:[color=green]
>> There you go... list comprehension. That is definatly nicer to look at.
>>
>>
>> "Elaine Jackson" <elainejackson7 355@home.com> wrote in message
>> news:zcxWb.4640 65$JQ1.270296@p d7tw1no...
>>[color=darkred]
>>>b=[x for x in b if x not in c]
>>>
>>>"Bart Nessux" <bart_nessux@ho tmail.com> wrote in message
>>>news:c0e4g3$ r1$1@solaris.cc .vt.edu...
>>>| By using lists, I can create sets of number. Suppose I have three lists.
>>>| One list is the super-set, one is a set that contains all the numbers
>>>| (just like the super-set) and the last is sub-set of the super-set. For
>>>| example:
>>>|
>>>| a = [1,2,3,4,5] # The super-set.
>>>| b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
>>>| c = [2,4] # A sub-set
>>>|
>>>| I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
>>>| this would make the sets look like this:
>>>|
>>>| a = [1,2,3,4,5]
>>>| b = [1,3,5]
>>>| c = [2,4]
>>>|
>>>| How do I test set c to find what it contains and then look at set b to
>>>| see if it contains any of those same numbers, and if so, remove them.
>>>|[/color][/color][/color]

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet?
--
Aahz (aahz@pythoncra ft.com) <*> http://www.pythoncraft.com/

"Argue for your limitations, and sure enough they're yours." --Richard Bach

**Peter Otten** · Jul 18 '05, 08:22 AM

Re: sets and subsets

Bart Nessux wrote:
[color=blue]
> Peter Otten wrote:[color=green]
>> Bart Nessux wrote:
>>
>>[color=darkred]
>>>By using lists, I can create sets of number. Suppose I have three lists.
>>>One list is the super-set, one is a set that contains all the numbers
>>>(just like the super-set) and the last is sub-set of the super-set. For
>>>example:
>>>
>>>a = [1,2,3,4,5] # The super-set.
>>>b = [1,2,3,4,5] # Looks just like the super-set, but it's not.
>>>c = [2,4] # A sub-set
>>>
>>>I'd like to remove 2 & 4 from set b BECAUSE they are present in set c...
>>>this would make the sets look like this:
>>>
>>>a = [1,2,3,4,5]
>>>b = [1,3,5]
>>>c = [2,4]
>>>
>>>How do I test set c to find what it contains and then look at set b to
>>>see if it contains any of those same numbers, and if so, remove them.[/color]
>>
>>
>> You want set operations, so why would you use lists?[/color]
>
> All my data are in lists:[/color]

All my beer is in sieves.
[color=blue]
>
> inputFile = file('ips.txt', 'r') #Super-set
> include = inputFile.readl ines()
> inputFile.close ()
>
> # The file below is compiled manually by hand... add IPs to it
> # whenever you want to exclude them from IP_protection.
> readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
> exclude = readFile.readli nes()
> readFile.close( )
>
> include = [x for x in include if x not in exclude] #Magic of Elaine
>
> outputFile = file('pruned_ip s.txt' , 'w')
> for i in include:
> print>> outputFile, i,
> outputFile.clos e()[/color]

(untested)
from sets import set

inputFile = file('ips.txt', 'r') #Super-set
include = Set(inputFile.r eadlines())
inputFile.close ()

readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
exclude = Set(readFile.re adlines())
readFile.close( )

# No Magic of Elaine

outputFile = file('pruned_ip s.txt' , 'w')
for i in include - exclude:
print >> outputFile, i,
outputFile.clos e()

Peter

**François Pinard** · Jul 18 '05, 08:22 AM

Re: sets and subsets

[Peter Otten]
[color=blue]
> (untested)
> from sets import set[/color]
[color=blue]
> inputFile = file('ips.txt', 'r') #Super-set
> include = Set(inputFile.r eadlines())
> inputFile.close ()[/color]
[color=blue]
> readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
> exclude = Set(readFile.re adlines())
> readFile.close( )[/color]
[color=blue]
> # No Magic of Elaine[/color]
[color=blue]
> outputFile = file('pruned_ip s.txt' , 'w')
> for i in include - exclude:
> print >> outputFile, i,
> outputFile.clos e()[/color]

Here is an equivalent, shorter algorithm (tested):

from sets import Set
file('pruned_ip s.txt', 'w').writelines (
Set(file('ips.t xt')) - Set(file('exclu ded_ips.txt')))

This code relies on `writelines' accepting an iterable, sets returning
their members whenever iterated, Set constructors accepting an iterable,
and files returning their lines whenever iterated. And of course, on
`close' rarely being needed in Python! :-)

The order of lines in the produced file is kind of random, however.

--
François Pinard http://www.iro.umontreal.ca/~pinard

**Bart Nessux** · Jul 18 '05, 08:23 AM

Re: sets and subsets

Peter Otten wrote:
[color=blue]
> outputFile = file('pruned_ip s.txt' , 'w')
> for i in include - exclude:
> print >> outputFile, i,
> outputFile.clos e()[/color]

Wow! That makes a lot more sense than the list comprehension stuff. I think
I'll use it. Thanks!

**Bart Nessux** · Jul 18 '05, 08:23 AM

Re: sets and subsets

François Pinard wrote:[color=blue]
> [Peter Otten]
>
>[color=green]
>>(untested)
>>from sets import set[/color]
>
>[color=green]
>>inputFile = file('ips.txt', 'r') #Super-set
>>include = Set(inputFile.r eadlines())
>>inputFile.clo se()[/color]
>
>[color=green]
>>readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
>>exclude = Set(readFile.re adlines())
>>readFile.clos e()[/color]
>
>[color=green]
>># No Magic of Elaine[/color]
>
>[color=green]
>>outputFile = file('pruned_ip s.txt' , 'w')
>>for i in include - exclude:
>> print >> outputFile, i,
>>outputFile.cl ose()[/color]
>
>
> Here is an equivalent, shorter algorithm (tested):
>
> from sets import Set
> file('pruned_ip s.txt', 'w').writelines (
> Set(file('ips.t xt')) - Set(file('exclu ded_ips.txt')))
>
> This code relies on `writelines' accepting an iterable, sets returning
> their members whenever iterated, Set constructors accepting an iterable,
> and files returning their lines whenever iterated. And of course, on
> `close' rarely being needed in Python! :-)
>
> The order of lines in the produced file is kind of random, however.
>[/color]

Wow! Sets are awesome. I was thinking in terms of lists. A list is like
a set and a set is like a list, but depending on the task at hand, they
have very different applications. Sets work great when one has a
super-set and two sub-sets that need to be compared and modified based
on what they contain and what the super-set contains.

Sets are straight-forward and easy to use too... I can always tell when
I'm trying to do something with a tool that wasn't designed to do what
I'm attempting to do (in this case lists). The task becomes complex and
tedious. Forget about trying to read the code a couple of weeks from now.

Thanks to all for the info on sets!

**Dave K** · Jul 18 '05, 08:24 AM

Re: sets and subsets

On Wed, 11 Feb 2004 18:57:15 -0500 in comp.lang.pytho n, François
Pinard <pinard@iro.umo ntreal.ca> wrote:
[color=blue]
>[Peter Otten]
>[color=green]
>> (untested)
>> from sets import set[/color]
>[color=green]
>> inputFile = file('ips.txt', 'r') #Super-set
>> include = Set(inputFile.r eadlines())
>> inputFile.close ()[/color]
>[color=green]
>> readFile = file('excluded_ ips.txt', 'r') #Sub-set to exclude
>> exclude = Set(readFile.re adlines())
>> readFile.close( )[/color]
>[color=green]
>> # No Magic of Elaine[/color]
>[color=green]
>> outputFile = file('pruned_ip s.txt' , 'w')
>> for i in include - exclude:
>> print >> outputFile, i,
>> outputFile.clos e()[/color]
>
>Here is an equivalent, shorter algorithm (tested):
>
>from sets import Set
>file('pruned_i ps.txt', 'w').writelines (
> Set(file('ips.t xt')) - Set(file('exclu ded_ips.txt')))
>
>This code relies on `writelines' accepting an iterable, sets returning
>their members whenever iterated, Set constructors accepting an iterable,
>and files returning their lines whenever iterated. And of course, on
>`close' rarely being needed in Python! :-)
>
>The order of lines in the produced file is kind of random, however.[/color]

That's very compact and neat, but for completeness I'd like to point
out that it could also be written (more clumsily) in one line with
list comprehensions, retaining the same order of elements as in the
original list:

file('pruned_ip s.txt', 'w').writelines ([ip for ip in file('ips.txt')
if ip not in file('excluded_ ips.txt')])

Of course, your example using sets is much clearer, so I prefer that.

Dave

**Tim Roberts** · Jul 18 '05, 08:26 AM

Re: sets and subsets

aahz@pythoncraf t.com (Aahz) wrote:[color=blue]
>
>[content at *bottom*]
>...
>A: Because it messes up the order in which people normally read text.
>Q: Why is top-posting such a bad thing?
>A: Top-posting.
>Q: What is the most annoying thing on usenet?[/color]

You know, it may be time for this crusade to end. What you say is entirely
valid if a single Usenet post is read out of context. However, when using
a threaded newsreader, as 90% of us do, top-posting allows me to read the
new content without moving my eyes. I just press N, N, N to move to the
next message and scan the new content at the top of the message. In this
particular thread, the content quickly grew larger than my newsreader's
preview pane, so bottom-posting requires me to move the focus to the
preview pane and scroll down to read.

Besides, the MOST annoying thing on Usenet is HTML posts.
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

sets and subsets

sets and subsets

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