R help - Aug 2006 - Escaping " ' " character

Dear all:

I have a character object x with ' (single-quote)
character.

x <- c('"hydrolase activity","actin
binding","3',5'-cyclic-nucleotide phosphodiesterase
activity")

I want to write a function that will identify ' and
replaces with \' 

myf <- function(term){
if (grep("'",term))
{ sub("'","\'",term)}
 }
> myf(x)
[1] "hydrolase activity"
[2] "actin binding"
[3] "3',5'-cyclic-nucleotide phosphodiesterase
activity"


In the result "3',5'" is remains unchaned. I expected
that to "3\',5\'-cyclic-nucleotide phosphodiesterase
activity". 

Could any one help me here. 
Thank you.



The reason I am asking is, I have to run another
function to make PREPARE statements for postgresql. 

Example:
"EXECUTE fetch_count_fterm_sql('hydrolase activity');"
                                                      
                 "EXECUTE fetch_count_fterm_sql('actin
binding');"
"EXECUTE
fetch_count_fterm_sql('3',5'-cyclic-nucleotide
phosphodiesterase activity');"

Here the last query statement will raise an exception
and my program fails from there. 

for instance:

mydb=# EXECUTE
fetch_count_fterm_sql('3',5'-cyclic-nucleotide
phosphodiesterase activity');
ERROR:  syntax error at or near "'-cyclic-nucleotide
phosphodiesterase activity'" at character 36



mydb=# EXECUTE
fetch_count_fterm_sql('3\',5\'-cyclic-nucleotide
phosphodiesterase activity');
 count
-------
    17
(1 row)

On Mon, 2006-08-21 at 13:43 -0700, Srinivas Iyyer wrote:
> Dear all:
> 
> I have a character object x with ' (single-quote)
> character.
> 
> x <- c('"hydrolase activity","actin
> binding","3',5'-cyclic-nucleotide phosphodiesterase
> activity")
> 
> I want to write a function that will identify ' and
> replaces with \' 
> 
> myf <- function(term){
> if (grep("'",term))
> { sub("'","\'",term)}
>  }
> > myf(x)
> [1] "hydrolase activity"
> [2] "actin binding"
> [3] "3',5'-cyclic-nucleotide phosphodiesterase
> activity"
> 
> 
> In the result "3',5'" is remains unchaned. I expected
> that to "3\',5\'-cyclic-nucleotide phosphodiesterase
> activity". 
> 
> Could any one help me here. 
> Thank you.
<snip>

Srini,

Try this:

 x <- "3',5'-cyclic-nucleotide phosphodiesterase activity"
> x
[1] "3',5'-cyclic-nucleotide phosphodiesterase activity"
> gsub("'", "\\\\'", x)
[1] "3\\',5\\'-cyclic-nucleotide phosphodiesterase activity"


Note that I use gsub() to replace both instances of the ', whereas sub()
will only replace the first.

The escape character itself needs to be escaped when used within the
replacement regex, since the "\" is a metacharacter. You end up with
four "\"s since R also treats the "\" specially.

When you cat() the output, you get:
> x.new
[1] "3\\',5\\'-cyclic-nucleotide phosphodiesterase activity"
> cat(x.new, "\n")
3\',5\'-cyclic-nucleotide phosphodiesterase activity


HTH,

Marc Schwartz