R help - Nov 2010 - How to program an error into an if-then statement

Hello!

I am running a loop (for a range of dates) and in this loop I am
reading in different files - based on a date that is part of the file
name.
However, for some of the dates, I have no file (no way to know which
dates). So, when I try to read it in I get an error:

Error in file(file, "rt") : cannot open the connection

Question: I'd like to program an if-then statement in my code that
says something like this:

myfile<-read.csv(myfilename)
if "cannot open the connection" - then do X

What statement should I use under "if"?

Thanks a lot!


-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com

Take a look in ?try and ?tryCatch

myfile <- tryCatch(read.csv(myfilename), error = invisible)
myfile$message


On Tue, Nov 9, 2010 at 2:55 PM, Dimitri Liakhovitski <
dimitri.liakhovitski@gmail.com> wrote:
> Hello!
>
> I am running a loop (for a range of dates) and in this loop I am
> reading in different files - based on a date that is part of the file
> name.
> However, for some of the dates, I have no file (no way to know which
> dates). So, when I try to read it in I get an error:
>
> Error in file(file, "rt") : cannot open the connection
>
> Question: I'd like to program an if-then statement in my code that
> says something like this:
>
> myfile<-read.csv(myfilename)
> if "cannot open the connection" - then do X
>
> What statement should I use under "if"?
>
> Thanks a lot!
>
>
> --
> Dimitri Liakhovitski
> Ninah Consulting
> www.ninah.com
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

	[[alternative HTML version deleted]]

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Dimitri Liakhovitski
> Sent: Tuesday, November 09, 2010 8:56 AM
> To: r-help
> Subject: [R] How to program an error into an if-then statement
> 
> Hello!
> 
> I am running a loop (for a range of dates) and in this loop I am
> reading in different files - based on a date that is part of the file
> name.
> However, for some of the dates, I have no file (no way to know which
> dates). So, when I try to read it in I get an error:
> 
> Error in file(file, "rt") : cannot open the connection
> 
> Question: I'd like to program an if-then statement in my code that
> says something like this:
> 
> myfile<-read.csv(myfilename)
> if "cannot open the connection" - then do X
> 
> What statement should I use under "if"?
> 
> Thanks a lot!
> 
> 
Rather than trying to read a non-existent file and generating an error,  you
might want to check if the file exists before trying to read it and take your
alternative action if it doesn't exist.  Check out

 ?file.exists

Hope this is helpful,

Dan

Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204