R help - Jun 2010 - RegExp question

Dear all,

I'm trying to filter out the "number of leaves" (it should be 1 in
the
example below) from the following string:
> string
[1] "Java-Object{J48 pruned tree\n------------------\n: 0 (15.0/3.0)\n
\nNumber of Leaves  : \t1\n\nSize of the tree : \t1\n}"

Any idea how to do that as simple as possible? Thanks in advance for
any advice.

Regards, Andrej

On Jun 16, 2010, at 12:04 PM, Andrej wrote:
> Dear all,
>
> I'm trying to filter out the "number of leaves" (it should be
1 in the
> example below) from the following string:
>
>> string
> [1] "Java-Object{J48 pruned tree\n------------------\n: 0 (15.0/3.0)\n
> \nNumber of Leaves  : \t1\n\nSize of the tree : \t1\n}"
>
> Any idea how to do that as simple as possible? Thanks in advance for
> any advice.
?sub   # or ?gsub if you need more than one pattern matched (they are  
on the same page).

This should find the first occurrence of digits following a tab  
terminated by a line feed and then return only the digits:

string <- "Java-Object{J48 pruned tree\n------------------\n: 0  
(15.0/3.0)\n \nNumber of Leaves  : \t1\n\nSize of the tree : \t1\n}"
sub("^.+\\t(\\d+)\\n.+$", "\\1", string)
[1] "1"

The parens within the search pattern are matched to "\\1". Need to  
double backslashed within patterns.
>
> Regards, Andrej
-- 

David Winsemius, MD
West Hartford, CT