# Is a merge interval function available?

Discussion in 'Python' started by Peng Yu, Feb 10, 2010.

1. ### Peng YuGuest

I'm wondering there is already a function in python library that can
merge intervals. For example, if I have the following intervals ('['
and ']' means closed interval as in
http://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_endpoints)

[1, 3]
[2, 9]
[10,13]
[11,12]

I want to get the following merged intervals.

[1,9]
[10,13]

Could somebody let me know if there is a function in the python
library?

Peng Yu, Feb 10, 2010

2. ### Steven D'ApranoGuest

On Wed, 10 Feb 2010 15:23:42 -0800, Peng Yu wrote:

> I'm wondering there is already a function in python library that can
> merge intervals. For example, if I have the following intervals ('[' and
> ']' means closed interval as in
> http://en.wikipedia.org/wiki/Interval_(mathematics)

#Excluding_the_endpoints)

Not in the standard library. There may be third-party libraries that do
it. Did you google "python interval"?

--
Steven

Steven D'Aprano, Feb 11, 2010

3. ### NobodyGuest

On Wed, 10 Feb 2010 15:23:42 -0800, Peng Yu wrote:

> I'm wondering there is already a function in python library that can
> merge intervals. For example, if I have the following intervals ('['
> and ']' means closed interval as in
> http://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_endpoints)
>
> [1, 3]
> [2, 9]
> [10,13]
> [11,12]
>
> I want to get the following merged intervals.
>
> [1,9]
> [10,13]
>
> Could somebody let me know if there is a function in the python
> library?

No, but try this:

def merge(intervals):
if not intervals:
return []
intervals = sorted(intervals, key = lambda x: x[0])
result = []
(a, b) = intervals[0]
for (x, y) in intervals[1:]:
if x <= b:
b = max(b, y)
else:
result.append((a, b))
(a, b) = (x, y)
result.append((a, b))
return result

Nobody, Feb 11, 2010
4. ### Steve HoldenGuest

Nobody wrote:
> On Wed, 10 Feb 2010 15:23:42 -0800, Peng Yu wrote:
>
>> I'm wondering there is already a function in python library that can
>> merge intervals. For example, if I have the following intervals ('['
>> and ']' means closed interval as in
>> http://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_endpoints)
>>
>> [1, 3]
>> [2, 9]
>> [10,13]
>> [11,12]
>>
>> I want to get the following merged intervals.
>>
>> [1,9]
>> [10,13]
>>
>> Could somebody let me know if there is a function in the python
>> library?

>
> No, but try this:
>
> def merge(intervals):
> if not intervals:
> return []
> intervals = sorted(intervals, key = lambda x: x[0])

Since Python uses lexical sorting and the intervals are lists isn't the
key specification redundant here?

> result = []
> (a, b) = intervals[0]
> for (x, y) in intervals[1:]:
> if x <= b:
> b = max(b, y)
> else:
> result.append((a, b))
> (a, b) = (x, y)
> result.append((a, b))
> return result
>

regards
Steve
--
Steve Holden +1 571 484 6266 +1 800 494 3119
PyCon is coming! Atlanta, Feb 2010 http://us.pycon.org/
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Steve Holden, Feb 11, 2010
5. ### Jonathan GardnerGuest

On Feb 10, 3:23 pm, Peng Yu <> wrote:
> I'm wondering there is already a function in python library that can
> merge intervals. For example, if I have the following intervals ('['
> and ']' means closed interval as inhttp://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_end...)
>
> [1, 3]
> [2, 9]
> [10,13]
> [11,12]
>
> I want to get the following merged intervals.
>
> [1,9]
> [10,13]
>
> Could somebody let me know if there is a function in the python
> library?

I vaguely recall a similar question a long time ago. Peng, is this a
homework assignment?

Perhaps we should add a standard module called "homework". It can have
functions for all the different homework assignments we see on
c.l.python. We can simply point people to this module and then can
include the code in their answers.

Jonathan Gardner, Feb 11, 2010
6. ### Alf P. SteinbachGuest

* Jonathan Gardner:
> On Feb 10, 3:23 pm, Peng Yu <> wrote:
>> I'm wondering there is already a function in python library that can
>> merge intervals. For example, if I have the following intervals ('['
>> and ']' means closed interval as inhttp://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_end...)
>>
>> [1, 3]
>> [2, 9]
>> [10,13]
>> [11,12]
>>
>> I want to get the following merged intervals.
>>
>> [1,9]
>> [10,13]
>>
>> Could somebody let me know if there is a function in the python
>> library?

>
> I vaguely recall a similar question a long time ago. Peng, is this a
> homework assignment?
>
> Perhaps we should add a standard module called "homework". It can have
> functions for all the different homework assignments we see on
> c.l.python. We can simply point people to this module and then can
> include the code in their answers.

If it's possible, there was/is this guy over in clc.c++ who responded/responds
to homework questions with the most advanced, convoluted and, except for

Cheers,

- Alf

Alf P. Steinbach, Feb 11, 2010
7. ### PeterGuest

On Feb 12, 8:03 am, Jonathan Gardner <>
wrote:
> On Feb 10, 3:23 pm, Peng Yu <> wrote:
>
>
>
>
>
> > I'm wondering there is already a function in python library that can
> > merge intervals. For example, if I have the following intervals ('['
> > and ']' means closed interval as inhttp://en.wikipedia.org/wiki/Interval_(mathematics)#Excluding_the_end...)

>
> > [1, 3]
> > [2, 9]
> > [10,13]
> > [11,12]

>
> > I want to get the following merged intervals.

>
> > [1,9]
> > [10,13]

>
> > Could somebody let me know if there is a function in the python
> > library?

>
> I vaguely recall a similar question a long time ago. Peng, is this a
> homework assignment?
>
> Perhaps we should add a standard module called "homework". It can have
> functions for all the different homework assignments we see on
> c.l.python. We can simply point people to this module and then can
> include the code in their answers.

Good idea - that would (also) give the teachers a convenient place to
check for what assignments have been solved by this list so they can
propose something else.

They can also grade the submissions against the code kept in this area
- exact copies could receive an "F" (for example )

Peter

Peter, Feb 11, 2010
8. ### NobodyGuest

On Wed, 10 Feb 2010 23:03:29 -0500, Steve Holden wrote:

>> intervals = sorted(intervals, key = lambda x: x[0])

>
> Since Python uses lexical sorting and the intervals are lists isn't the
> key specification redundant here?

Yes, but I wanted to make it explicit.

Well, omitting the key= would change the sorting order in the event that
multiple intervals have the same start, but it still won't affect the
result of the function overall.

Nobody, Feb 12, 2010