Get number from end of name

[Andrus]

I need to create function

static int ItemNumber(stri ng itemName)

which returns number from end of name

ItemNumber("Ite m1") returns 1
ItemNumber("Oth er1") returns 1
ItemNumber("Ite m123") returns 123


etc.
How to create this ?

Andrus.

[zacks@construction-imaging.com]

Re: Get number from end of name

On Aug 7, 12:09 pm, "Andrus" <kobrule...@hot .eewrote:

I need to create function  
>
static int ItemNumber(stri ng itemName)
>
which returns number from end of name
>
ItemNumber("Ite m1")  returns  1
ItemNumber("Oth er1")  returns  1
ItemNumber("Ite m123")  returns  123
>
etc.
How to create this ?
>
Andrus.

Loop through the string with the .Substring method specifying one
character at at time. Try to convert the character to a number in a
Try/Catch block. When the function is successful, then from that index
position on is the number, and you can pick it off with
another .Substring call.

[Jon Skeet [C# MVP]]

Re: Get number from end of name

On Aug 7, 5:16 pm, za...@construct ion-imaging.com wrote:

Loop through the string with the .Substring method specifying one
character at at time.

There's no point in creating loads of strings for no reason. Using the
indexer returns a char:

char c = text[i];

Try to convert the character to a number in a
Try/Catch block.

Ick no. Use Character.IsDig it - then you're not using exceptions for
flow control.

When the function is successful, then from that index
position on is the number, and you can pick it off with
another .Substring call.

No, that would fail on "foo5bar10" . We need to work back from the end.
I would suggest something like:

public static int ParseNumberAtEn d(string text)
{
for (int i = text.Length-1; i >= 0; i--)
{
if (!Character.IsD igit(text[i]))
{
if (i == text.Length - 1)
{
throw new ArgumentExcepti on("No digits at end");
}
string digits = text.Substring( i+1);
return int.Parse(digit s);
}
}
// Text is entirely made of digits!
return int.Parse(text) ;
}

Alternatively, Andrus could use a regex of something like @"\d
+^" (Possibly $ instead of ^ - I can never remember which way round
they go.)

Jon

[Ben Voigt [C++ MVP]]

Re: Get number from end of name

Alternatively, Andrus could use a regex of something like @"\d

+^" (Possibly $ instead of ^ - I can never remember which way round
they go.)

$ in this case, to anchor the end.
^ anchors the beginning.


LastIndexOfAny might also be a reasonable solution, though I would expect
Char.IsDigit to be faster.

>
Jon

[jake]

Re: Get number from end of name

Along the same lines as Jon's reply, here is a fun way if you are
using Framework 3.5:

int.Parse("0" +
item.Substring( Array.LastIndex Of<char>(item.T oCharArray(),
item.ToCharArra y().LastOrDefau lt<char>(c =!Char.IsDigit( c))) + 1))

Long line, but nice trick. Just an FYI.
jake


On Aug 7, 12:28 pm, "Jon Skeet [C# MVP]" <sk...@pobox.co mwrote:

On Aug 7, 5:16 pm, za...@construct ion-imaging.com wrote:
>

Loop through the string with the .Substring method specifying one
character at at time.

>
There's no point in creating loads of strings for no reason. Using the
indexer returns a char:
>
char c = text[i];
>

Try to convert the character to a number in a
Try/Catch block.

>
Ick no. Use Character.IsDig it - then you're not using exceptions for
flow control.
>

When the function is successful, then from that index
position on is the number, and you can pick it off with
another .Substring call.

>
No, that would fail on "foo5bar10" . We need to work back from the end.
I would suggest something like:
>
public static int ParseNumberAtEn d(string text)
{
for (int i = text.Length-1; i >= 0; i--)
{
if (!Character.IsD igit(text[i]))
{
if (i == text.Length - 1)
{
throw new ArgumentExcepti on("No digits at end");
}
string digits = text.Substring( i+1);
return int.Parse(digit s);
}
}
// Text is entirely made of digits!
return int.Parse(text) ;
>
}
>
Alternatively, Andrus could use a regex of something like @"\d
+^" (Possibly $ instead of ^ - I can never remember which way round
they go.)
>
Jon

[Peter Duniho]

Re: Get number from end of name

On Thu, 07 Aug 2008 10:05:18 -0700, Ben Voigt [C++ MVP]
<rbv@nospam.nos pamwrote:

>Alternativel y, Andrus could use a regex of something like @"\d
>+^" (Possibly $ instead of ^ - I can never remember which way round
>they go.)

>
$ in this case, to anchor the end.
^ anchors the beginning.
>
>
LastIndexOfAny might also be a reasonable solution, though I would expect
Char.IsDigit to be faster.

Of course, if faster was the priority, calling Parse() is probably not the
preferred solution anyway. Instead, one would just scan once from the end
to find the start of the numeric string, and then go forward again,
accumulating each digit and multiplying by 10 with each new one before
adding the current digit. In other words, basically the same as what
Jon's code does, but combining the substring extraction with the parsing,
and doing it all in the same method rather than calling into the classes
(and without instantiating an intermediate string). For example:

public static int ParseNumberAtEn d(string text)
{
int i = text.Length;
int result = 0;

while (--i >= 0 && Character.IsDig it(text[i])) { }

if (i == text.Length - 1)
{
throw new ArgumentExcepti on("No digits at end");
}

while (++i < text.Length)
{
result = result * 10 + text[i] - '0';
}

return result;
}

For maintainability , I like the RegEx suggestion. It keeps all the
looping/substring mechanics hidden from view, leaving just the semantics
of "parse the number at the end of the string".

I think using LastIndexOfAny( ) is a reasonable alternative to RegEx, if
one finds the RegEx syntax less-than-obvious, but then you'd be stuck with
the explicit call to Substring() before Parse().

How many other ways can we skin this cat? :)

Pete

[Paul E Collins]

Re: Get number from end of name

"Peter Duniho" <NpOeStPeAdM@nn owslpianmk.comw rote:

How many other ways can we skin this cat? :)

static int GetNumberAtEnd( string s)
{
int val = 0, pos = s.Length - 1;
while (pos 0 && s[pos] >= '0' && s[pos] <= '9')
{
val += (s[pos] - '0') * (int) Math.Pow(10, s.Length - pos - 1);
pos--;
}
return val;
}

Eq.

[Jon Skeet [C# MVP]]

Re: Get number from end of name

Peter Duniho <NpOeStPeAdM@nn owslpianmk.comw rote:

<snip>

How many other ways can we skin this cat? :)

Create a parameterised SQL query and get the query engine to do the
work? Or we could always set up a web service for it, and maybe write a
custom LINQ provider to call that web service.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Paul E Collins]

Re: Get number from end of name

"Jon Skeet [C# MVP]" <skeet@pobox.co mwrote:

Use Character.IsDig it

But are digits recognised by Char.IsDigit guaranteed to parse as integers?
Even on a Western system, Hebrew numerals would count as digits (in the
character sense), wouldn't they?

Eq.

[Jon Skeet [C# MVP]]

Re: Get number from end of name

Paul E Collins <find_my_real_a ddress@CL4.orgw rote:

"Jon Skeet [C# MVP]" <skeet@pobox.co mwrote:
>

Use Character.IsDig it

>
But are digits recognised by Char.IsDigit guaranteed to parse as integers?
Even on a Western system, Hebrew numerals would count as digits (in the
character sense), wouldn't they?

Hmm... not sure. It's only *decimal* digits, but I don't know what
other characters are in DecimalDigitNum ber.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Paul E Collins]

Re: Get number from end of name

"Jon Skeet [C# MVP]" <skeet@pobox.co mwrote:

But are digits recognised by Char.IsDigit guaranteed to parse as
integers? Even on a Western system, Hebrew numerals would count as
digits (in the character sense), wouldn't they?

>
Hmm... not sure. It's only *decimal* digits, but I don't know what other
characters are in DecimalDigitNum ber.

char ch = (char) 0x667; // Arabic-Indic Digit Seven
Console.WriteLi ne(Char.IsDigit (ch)); // "True"
int i = Int32.Parse(ch. ToString()); // throws FormatException

I suppose Int32.Parse *might* work differently depending on your system
locale, but in either case Char.IsDigit will check whether the character is
a digit in *any* locale, so it's not safe to use for this purpose.

Eq.

[Jon Skeet [C# MVP]]

Re: Get number from end of name

Paul E Collins <find_my_real_a ddress@CL4.orgw rote:

"Jon Skeet [C# MVP]" <skeet@pobox.co mwrote:
>

But are digits recognised by Char.IsDigit guaranteed to parse as
integers? Even on a Western system, Hebrew numerals would count as
digits (in the character sense), wouldn't they?

Hmm... not sure. It's only *decimal* digits, but I don't know what other
characters are in DecimalDigitNum ber.

>
char ch = (char) 0x667; // Arabic-Indic Digit Seven
Console.WriteLi ne(Char.IsDigit (ch)); // "True"
int i = Int32.Parse(ch. ToString()); // throws FormatException
>
I suppose Int32.Parse *might* work differently depending on your system
locale, but in either case Char.IsDigit will check whether the character is
a digit in *any* locale, so it's not safe to use for this purpose.

Yup. It's a shame there isn't a property for this, as it's reasonably
common.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com

[Ben Voigt [C++ MVP]]

Re: Get number from end of name

Jon Skeet [C# MVP] wrote:

Paul E Collins <find_my_real_a ddress@CL4.orgw rote:

>"Jon Skeet [C# MVP]" <skeet@pobox.co mwrote:
>>

>>>But are digits recognised by Char.IsDigit guaranteed to parse as
>>>integers? Even on a Western system, Hebrew numerals would count as
>>>digits (in the character sense), wouldn't they?
>>>
>>Hmm... not sure. It's only *decimal* digits, but I don't know what
>>other characters are in DecimalDigitNum ber.

>>
>char ch = (char) 0x667; // Arabic-Indic Digit Seven
>Console.WriteL ine(Char.IsDigi t(ch)); // "True"
>int i = Int32.Parse(ch. ToString()); // throws FormatException
>>
>I suppose Int32.Parse *might* work differently depending on your
>system locale, but in either case Char.IsDigit will check whether
>the character is a digit in *any* locale, so it's not safe to use
>for this purpose.

>
Yup. It's a shame there isn't a property for this, as it's reasonably
common.

Cue requests for extension properties.