Help with regular expression

9 Aug 2006 11:46 PM

Bob

I have numbers I am trying to match, for example:

input = "1.2.3.4"
pattern = @"\d+\.\d+\.\d+\.\d+"

But the problem is, three of them are optional and it is important which
ones get matched. The numbers need to be matched like this:

c
c.d
a.c.d
a.b.c.d

I can get close with this pattern:

pattern = @"(((?<a>\d+)\.)?(?\d+)\.)?(?<c>\d+)(\.(?<d>\d+))?"

But I can't seem to figure out how to make 'd' a higher priority than 'a'
and 'b, because with "2.3.4" it is matching a.b.c instead of a.c.d.

Any input would be appreciated...

10 Aug 2006 12:23 AM

Bob

Seems to me this pattern should do the trick:

input = "1.2.3.4"
pattern = @"\A((?<a>\d+)\.((?\d+)\.)??)??(?<c>\d+)(\.(?<d>\d+))?\Z";

And it does in most cases, but for some reason when all four numbers are
specified, it matches this:

a = "2"
b = ""
c = "3"
d = "4"

Looking through all the captures, it doesn't even match "1" at all. How can
this regular expression skip over "1"? I have the \A and \Z there, so if all
items weren't captured, it should fail, no?

Show quote

"Bob" <nob***@nowhere.com> wrote in message
news:uBWZV4AvGHA.3500@TK2MSFTNGP06.phx.gbl...
>I have numbers I am trying to match, for example:
>
> input = "1.2.3.4"
> pattern = @"\d+\.\d+\.\d+\.\d+"
>
> But the problem is, three of them are optional and it is important which
> ones get matched. The numbers need to be matched like this:
>
> c
> c.d
> a.c.d
> a.b.c.d
>
> I can get close with this pattern:
>
> pattern = @"(((?<a>\d+)\.)?(?\d+)\.)?(?<c>\d+)(\.(?<d>\d+))?"
>
> But I can't seem to figure out how to make 'd' a higher priority than 'a'
> and 'b, because with "2.3.4" it is matching a.b.c instead of a.c.d.
>
> Any input would be appreciated...
>
>
>
>

10 Aug 2006 1:18 AM

Bob

This is the only way I have been able to get this to work:

const String pattern = @"\A(((?<a>\d+)\.(?\d+)\.(?<c>\d+)\.(?<d>\d+))|" +
 @"((?<a>\d+)\.(?<c>\d+)\.(?<d>\d+))|" +
 @"((?<c>\d+)\.(?<d>\d+))|" +
 @"((?<c>\d+)))\Z";

If anybody has a better way, I would be interested in hearing of it.

Show quote

"Bob" <nob***@nowhere.com> wrote in message
news:ete$zMBvGHA.4612@TK2MSFTNGP02.phx.gbl...
> Seems to me this pattern should do the trick:
>
> input = "1.2.3.4"
> pattern = @"\A((?<a>\d+)\.((?\d+)\.)??)??(?<c>\d+)(\.(?<d>\d+))?\Z";
>
> And it does in most cases, but for some reason when all four numbers are
> specified, it matches this:
>
> a = "2"
> b = ""
> c = "3"
> d = "4"
>
> Looking through all the captures, it doesn't even match "1" at all. How
> can this regular expression skip over "1"? I have the \A and \Z there, so
> if all items weren't captured, it should fail, no?
>
>
> "Bob" <nob***@nowhere.com> wrote in message
> news:uBWZV4AvGHA.3500@TK2MSFTNGP06.phx.gbl...
>>I have numbers I am trying to match, for example:
>>
>> input = "1.2.3.4"
>> pattern = @"\d+\.\d+\.\d+\.\d+"
>>
>> But the problem is, three of them are optional and it is important which
>> ones get matched. The numbers need to be matched like this:
>>
>> c
>> c.d
>> a.c.d
>> a.b.c.d
>>
>> I can get close with this pattern:
>>
>> pattern = @"(((?<a>\d+)\.)?(?\d+)\.)?(?<c>\d+)(\.(?<d>\d+))?"
>>
>> But I can't seem to figure out how to make 'd' a higher priority than 'a'
>> and 'b, because with "2.3.4" it is matching a.b.c instead of a.c.d.
>>
>> Any input would be appreciated...
>>
>>
>>
>>
>
>

10 Aug 2006 12:31 PM

Kevin Spencer

You're going to have t define your rules better than that. You cannot define
a rule set by an example. The example you gave shows 4 numbers delimited by
periods, but it doesn't state whether the periods are decimal places,
whether the decimal places are between digits in the same numbers, or,
perhaps, whether the numbers will always be delimited by single periods,
doubled periods, or perhaps by any other character. In addition, you use
variables (a,b,c,d) to refer to something about some rule, but do not
associate them specifically. And your regular expression seems to imply that
there will always be four groups of 1 or more digits, delimited by single
periods, but you have not stated this.

A regular expression, like any programming solution, is an expression of a
process that defines and follows a set of logical rules. To solve the
problem, the problem must be fully defined to begin with. In my experience,
defining the problem fully often points directly to the solution.

--
HTH,

Kevin Spencer
Microsoft MVP
Chicken Salad Surgery

Accept the Unexpected.

Show quote

"Bob" <nob***@nowhere.com> wrote in message
news:uBWZV4AvGHA.3500@TK2MSFTNGP06.phx.gbl...
>I have numbers I am trying to match, for example:
>
> input = "1.2.3.4"
> pattern = @"\d+\.\d+\.\d+\.\d+"
>
> But the problem is, three of them are optional and it is important which
> ones get matched. The numbers need to be matched like this:
>
> c
> c.d
> a.c.d
> a.b.c.d
>
> I can get close with this pattern:
>
> pattern = @"(((?<a>\d+)\.)?(?\d+)\.)?(?<c>\d+)(\.(?<d>\d+))?"
>
> But I can't seem to figure out how to make 'd' a higher priority than 'a'
> and 'b, because with "2.3.4" it is matching a.b.c instead of a.c.d.
>
> Any input would be appreciated...
>
>
>
>