help with tryCatch

Henrik,
Please, stay with me.
there is a problem with the way tryCatch processes statements and that
is exactly what the help file does not describe at all. I am trying

************************
catch=function(vec){
  ans=NULL;err=NULL;
  for (i in vec) {
  tryCatch({
      source(i);
      ans=c(ans,i);
      cat(ans," from try");
  },
  error=function(er){
    cat(i," from catch\n");
    err=c(err,i);

  }
           )

}
  ret=list(ans=ans,err=err)
  ret
}

v=c("gdhfdh","hdhdfjh")  #non-existent files
ret=catch(v)  # err is NULL and none of the statements in that block is
executed ??

below is a Java example that executes the catch block as it should. How
can I achieve the same in R?
***************************
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Vector;

public class ReadFiles {

    public static void main(String[] args) {
        String[] files={"asdf","qwert"};
        Vector err=new Vector();
        FileReader inputStream = null;
        for (int j=0;j<2;j++){
            try {
                inputStream = new FileReader(files[j]);
                int c;
                while ((c = inputStream.read()) != -1) {}
            } catch(IOException e){
                err.add(j,files[j]); // this statement executes!
            } finally {
                if (inputStream != null) {
                    inputStream.close(); // IO not encapsulated here,
but declared in "main throws". pls ignore since "source(arg)" in R takes
care of closing.
                }
            }
        }
        for (Object j:err){
        System.out.println(j);
    }
    }
}









Henrik Bengtsson wrote:

To be more precise, put the tryCatch() only around the code causing
the problem, i.e. around source().  /H

On 2/13/07, Henrik Bengtsson <hb at stat.berkeley.edu> wrote:

Put the for loop outside the tryCatch(). /H

On 2/13/07, Stephen Bond <sje at mast.queensu.ca> wrote:

Henrik,

thank you for the reference. Can you please tell me why the following
does not work?

vec=c("hdfhjfd","jdhfhjfg")    # non-existent file names
catch=function(vec){
  tryCatch({
    ans =NULL;err=NULL;
    for (i in vec) {
      source(i)
      ans=c(ans,i)
    }
  },
  interrupt=function(ex){print(ex)},
  error=function(er){
     print(er)
     cat(i,"\n")
     err=c(err,i)
  },
  finally={
    cat("finish")
  }
 ) #tryCatch
}

catch(vec) # throws an error after the first file and stops there

while

I want it to go through the list and accumulate the nonexistent
filenames in err.

Thank you
Stephen

Henrik Bengtsson wrote:

Hi,

google "R tryCatch example" and you'll find:

 http://www.maths.lth.se/help/R/ExceptionHandlingInR/

Hope this helps

Henrik

On 2/13/07, Stephen Bond <sje at mast.queensu.ca> wrote:

Henrik,

I had looked at tryCatch before posting the question and asked the
question because the help file was not adequate for me. Could

you pls

provide a sample code of
try{ try code}
catch(error){catch code}

let's say you have a vector of local file names and want to

source them

encapsulating in a tryCatch to avoid the skipping of all good

file names

after a bad file name.

thank you
stephen


Henrik Bengtsson wrote:

See ?tryCatch. /Henrik

On 2/12/07, Stephen Bond <sje at mast.queensu.ca> wrote:

Could smb please help with try-catch encapsulating a function

for

downloading. Let's say I have a character vector of symbols and

want to

download each one and surround by try and catch to be safe

# get.hist.quote() is in library(tseries), but the question

does not

depend on it, I could be sourcing local files instead

ans=null;error=null;
for ( sym in sym.vec){
try(ans=cbind(ans,get.hist.quote(sym,start=start)))

#accumulate in

a zoo

matrix
catch(theurlerror){error=c(error,sym)} #accumulate failed

symbols

}

I know the code above does not work, but it conveys the idea.

tryCatch

help page says it is similar to Java try-catch, but I know

how to

do a

try-catch in Java and still can't do it in R.

Thank you very much.
stephen

code.