R help - May 2012 - Inf and lazy evaluation

Hi,

I have a question involving Inf, lazy evaluation, and maybe argument
recycling.  I have a directory where I am trying to check for the
existence of files of a certain pattern, basically something like
"filename-#", where # is an integer.  I can do something like this,
which works.

file.exists(paste(filename, "-", 1:100, sep = ""))

But I don't like the fact that I am only checking the first 100
possibilities.  What I would prefer is this:

file.exists(paste(filename, "-", 1:Inf, sep = ""))

But that doesn't work, I get the error:

Error in 1:Inf : result would be too long a vector

On one hand, with lazy evaluation, you would think that 1:Inf should
work.  On the other hand, I'm not quite sure what the output would be
if it was working, especially if there were large gaps in the
integers.  Is there a way to get the behavior I seek (i.e. the lazy
evaluation of 1:Inf).

Thanks,


James

R is lazy, but not quite that lazy ;-)

It's likely much easier to do this with regexps

something like

list.files()[grepl(paste0(filename, "-"[0123456789]+""),
list.files())]

Michael


On Mon, May 14, 2012 at 3:34 PM, J Toll <jctoll at gmail.com>
wrote:
> Hi,
>
> I have a question involving Inf, lazy evaluation, and maybe argument
> recycling. ?I have a directory where I am trying to check for the
> existence of files of a certain pattern, basically something like
> "filename-#", where # is an integer. ?I can do something like
this,
> which works.
>
> file.exists(paste(filename, "-", 1:100, sep = ""))
>
> But I don't like the fact that I am only checking the first 100
> possibilities. ?What I would prefer is this:
>
> file.exists(paste(filename, "-", 1:Inf, sep = ""))
>
> But that doesn't work, I get the error:
>
> Error in 1:Inf : result would be too long a vector
>
> On one hand, with lazy evaluation, you would think that 1:Inf should
> work. ?On the other hand, I'm not quite sure what the output would be
> if it was working, especially if there were large gaps in the
> integers. ?Is there a way to get the behavior I seek (i.e. the lazy
> evaluation of 1:Inf).
>
> Thanks,
>
>
> James
>
> ______________________________________________
> R-help at 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.

?list.files


-- Bert

On Mon, May 14, 2012 at 12:34 PM, J Toll <jctoll at gmail.com>
wrote:
> Hi,
>
> I have a question involving Inf, lazy evaluation, and maybe argument
> recycling. ?I have a directory where I am trying to check for the
> existence of files of a certain pattern, basically something like
> "filename-#", where # is an integer. ?I can do something like
this,
> which works.
>
> file.exists(paste(filename, "-", 1:100, sep = ""))
>
> But I don't like the fact that I am only checking the first 100
> possibilities. ?What I would prefer is this:
>
> file.exists(paste(filename, "-", 1:Inf, sep = ""))
>
> But that doesn't work, I get the error:
>
> Error in 1:Inf : result would be too long a vector
>
> On one hand, with lazy evaluation, you would think that 1:Inf should
> work. ?On the other hand, I'm not quite sure what the output would be
> if it was working, especially if there were large gaps in the
> integers. ?Is there a way to get the behavior I seek (i.e. the lazy
> evaluation of 1:Inf).
>
> Thanks,
>
>
> James
>
> ______________________________________________
> R-help at 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.


-- 

Bert Gunter
Genentech Nonclinical Biostatistics

Internal Contact Info:
Phone: 467-7374
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