Groups > comp.soft-sys.math.mathematica > #3488

Re: Operations on RegularExpression matches

From	Albert Retey <awnl@gmx-topmail.de>
Newsgroups	comp.soft-sys.math.mathematica
Subject	Re: Operations on RegularExpression matches
Date	2011-07-05 09:10 +0000
Organization	Steven M. Christensen and Associates, Inc and MathTensor, Inc.
Message-ID	<iuukdh$eln$1@smc.vnet.net> (permalink)
References	<ius5nq$2g4$1@smc.vnet.net>

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Hi,
>
> I have string of all lower case letters:
>
> 	string = "this is a string"
>
> I wish to capitalize the first letter:
>
> 	StringReplace[string, StartOfString ~~ x_ ->  ToUpperCase[x]]  (* Does want I want *)
>
> Now I try to do the same thing using RegularExpression:
>
> 	StringReplace[string, RegularExpression["(^.)"] ->  ToUpperCase["$1"]]
>
> which fails (returns original string without capitalization).
>
> I know the match is occurring since
>
> 	StringReplace[string, RegularExpression["(^.)"] ->  ToUpperCase["$1X"]]
>
> returns
>
> 	"tXhis is a string"
>
> What am I missing about using the matched part of a regular expression?

the problem is that ToUpperCase is done on the pattern, not the match. 
You need RuleDelayed so that ToUpperCase is done on the matching string:

StringReplace[string, RegularExpression["(^.)"] :> ToUpperCase["$1"]]

this is not necessary with the StringExpression approach since then 
ToUpperCase[x] remains unevaluated since x is no string.

hth,

albert

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Operations on RegularExpression matches Jon Joseph <josco.jon@gmail.com> - 2011-07-04 10:47 +0000
  Re: Operations on RegularExpression matches "Oleksandr Rasputinov" <oleksandr_rasputinov@hmamail.com> - 2011-07-05 09:15 +0000
  Re: Operations on RegularExpression matches Albert Retey <awnl@gmx-topmail.de> - 2011-07-05 09:10 +0000

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