R help - Nov 2012 - Problems understanding use of regular expression (in gsub) for manipulating currency

Hello,

After reading help file, various threads on this board, and other online
tutorials, I've attempted to use gsub (using Perl-like syntax) to change a
currency string into something that can be converted to numeric type using only
one regular expression.  Can anybody point out my error?  Note that

>  x <- "\"$ 1,200,300,400.50\""
Tried the following in an attempt to arrive at "1200300400.50"
>  gsub("(^[\\D]*)(([\\d]*)[,])*([\\d]*[.]*[\\d]*)([\\D]*)",
"\\3\\4", x, perl=TRUE)
[1]  "300400.50"

Note that "\d" matches a digit character and "\D" matches a
non-digit character.
Results group "\2" was intentionally omitted from the replacement
pattern as it would have included commas.

I was expecting multiple results for group "\3"

Many thanks,
Mauricio

	[[alternative HTML version deleted]]

On Nov 21, 2012, at 1:41 PM, Mauricio Cornejo wrote:
> Hello,
> 
> After reading help file, various threads on this board, and other online
tutorials, I've attempted to use gsub (using Perl-like syntax) to change a
currency string into something that can be converted to numeric type using only
one regular expression.  Can anybody point out my error?  Note that
> 
> 
>>   x <- "\"$ 1,200,300,400.50\""
> 
> Tried the following in an attempt to arrive at "1200300400.50"
> 
>>   gsub("(^[\\D]*)(([\\d]*)[,])*([\\d]*[.]*[\\d]*)([\\D]*)",
"\\3\\4", x, perl=TRUE)
> [1]  "300400.50"
> 
> Note that "\d" matches a digit character and "\D"
matches a non-digit character.
> Results group "\2" was intentionally omitted from the replacement
pattern as it would have included commas.
> gsub("[,\"]", "", gsub("^\\D*(\\d.*)",
"\\1",x, perl=TRUE) )
[1] "1200300400.50"


I have my doubts about the "\"..." construction. I suspect it
stems from your not understanding the conventaion used in printing escpae
characters in R.


-- 

David Winsemius, MD
Alameda, CA, USA

Arun, thanks for both of your suggestions.

I played with your second idea some more and seemed to have found a more general
solution (If not a digit nor period then replace with blank).


 x <- "\"$ 1,200,300,400.50\""
 gsub("[^0-9|.]", "", x, perl=TRUE)
[1] "1200300400.50"

Regards,
Mauricio



________________________________


Cc: R help <r-help@r-project.org> 
Sent: Wednesday, November 21, 2012 5:26 PM
Subject: Re: [R] Problems understanding use of regular expression (in gsub) for
manipulating currency

HI,
One more method:
x <- "\"$ 1,200,300,400.50\""
 gsub("[\",$ ]","",x)
#[1] "1200300400.50"
A.K.




----- Original Message -----

To: "r-help@r-project.org" <r-help@r-project.org>
Cc: 
Sent: Wednesday, November 21, 2012 4:41 PM
Subject: [R] Problems understanding use of regular expression (in gsub) for
manipulating currency

Hello,

After reading help file, various threads on this board, and other online
tutorials, I've attempted to use gsub (using Perl-like syntax) to change a
currency string into something that can be converted to numeric type using only
one regular expression.  Can anybody point out my error?  Note that

>  x <- "\"$ 1,200,300,400.50\""
Tried the following in an attempt to arrive at "1200300400.50"
>  gsub("(^[\\D]*)(([\\d]*)[,])*([\\d]*[.]*[\\d]*)([\\D]*)",
"\\3\\4", x, perl=TRUE)
[1]  "300400.50"

Note that "\d" matches a digit character and "\D" matches a
non-digit character.
Results group "\2" was intentionally omitted from the replacement
pattern as it would have included commas.

I was expecting multiple results for group "\3"

Many thanks,
Mauricio

    [[alternative HTML version deleted]]


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	[[alternative HTML version deleted]]

Here is another approach:
> x <- "\"$ 1,200,300,400.50\""
>  x
[1] "\"$ 1,200,300,400.50\""
> gsub("[,$ \"]", "", x)
[1] "1200300400.50"
> as.numeric(gsub("[,$ \"]", "", x))
[1] 1200300401
>

On Wed, Nov 21, 2012 at 4:41 PM, Mauricio Cornejo
<mauriciocornejo at yahoo.com> wrote:
> x <- "\"$ 1,200,300,400.50\""


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.