On 8/17/2011 11:13 AM, Uwe Ligges wrote:
Actually require() is a wrapper around library() with more error
handling to be used inside other functions. Just type require(), you can
read the few lines of code quickly.
I think the unstated corollary is that library() is preferred when not
inside a function, but within a file that might be sourced. That is
because if the package can not be loaded, execution will halt at that
point. If require were used, then execution would continue, almost
certainly unsuccessfully. Compare two files:
library("nonexistant")
print("done")
versus
require("nonexistant")
print("done")
Sourcing the first gives:
Error in library("nonexistant") :
there is no package called 'nonexistant'
Sourcing the second gives:
Loading required package: nonexistant
[1] "done"
Warning message:
In library(package, lib.loc = lib.loc, character.only = TRUE,
logical.return = TRUE, :
there is no package called 'nonexistant'
Maybe put another way, if you aren't going to do anything with the
return value of require, then you are probably better off using library
so it fails sooner.
Uwe Ligges
On 17.08.2011 19:57, Nordlund, Dan (DSHS/RDA) wrote:
-----Original Message-----
From: istaz...@gmail.com [mailto:istaz...@gmail.com] On Behalf Of Ista
Zahn
Sent: Wednesday, August 17, 2011 10:12 AM
To: Nordlund, Dan (DSHS/RDA)
Cc: r-help@r-project.org
Subject: Re: [R] Using require() vs. library()
Hi Dan,
Is there something you would like to know that is not covered by
help(library) ?
Best,
Ista
On Wed, Aug 17, 2011 at 12:40 PM, Nordlund, Dan (DSHS/RDA)
<nord...@dshs.wa.gov> wrote:
A recent post prompts me to ask this question. Is there any reason
to prefer using library() over require()? I tend to use require()
instead of library() to load packages, but I wonder if there are
situations where it would be better to use library().
Well, I guess when I read that "require is designed for use inside
other functions..." I wasn't sure if that meant there might be times
when it would be better to use library when not inside other
functions. But maybe it was more generally a question about style,
prompted by a post responding to the common confusion between the
terms 'package' and 'library' amongst those new to R. To me, it always
seemed more natural type require(my.package) than library(my.package).
I just wanted to make sure I wasn't missing something that might make
me regret that choice.
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
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