[R-sig-hpc] Quickest way to make a large "empty" file on disk?

[Simon Urbanek]

On May 2, 2012, at 6:23 PM, Jonathan Greenberg wrote:

> R-helpers:
> 
> What would be the absolute fastest way to make a large "empty" file (e.g.
> filled with all zeroes) on disk, given a byte size and a given number
> number of empty values.  I know I can use writeBin, but the "object" in
> this case may be far too large to store in main memory.  I'm asking because
> I'm going to use this file in conjunction with mmap to do parallel writes
> to this file.  Say, I want to create a blank file of 10,000 floating point
> numbers.
> 

The most trivial way is to simply seek to the end and write a byte:

> n=100000
>  f=file("foo","wb")
> seek(f,n-1)
[1] 0
> writeBin(raw(1),f)
> close(f)
> file.info("foo")$size
[1] 1e+05

Cheers,
Simon


> Thanks!
> 
> --j
> 
> -- 
> Jonathan A. Greenberg, PhD
> Assistant Professor
> Department of Geography and Geographic Information Science
> University of Illinois at Urbana-Champaign
> 607 South Mathews Avenue, MC 150
> Urbana, IL 61801
> Phone: 415-763-5476
> AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007
> http://www.geog.illinois.edu/people/JonathanGreenberg.html
> 
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