[R] if/else help

Crombie, Burnette N bcrombie at utk.edu
Wed Sep 21 17:38:15 CEST 2016

Thank you for your time, Don.  Exactly what I was looking for - a one-liner.  Feedback from others on this post has been good to expand my knowledge, though.  I'm too old for homework but have just started using R if/else, loops, and functions and trying to get the hang of them.  Best wishes - B

-----Original Message-----
From: MacQueen, Don [mailto:macqueen1 at llnl.gov] 
Sent: Wednesday, September 21, 2016 11:26 AM
To: Crombie, Burnette N <bcrombie at utk.edu>; r-help at r-project.org
Subject: Re: [R] if/else help

Hopefully this is not a homework question.

The other responses are fine, but I would suggest the simplest way to do exactly what you ask is

if (!exists('r4')) r4 <- data.frame(a=0, b=0, c=0, d='x')

The exists() function requires a character string for its first argument, i.e., the name of the object, not the object itself (check the help page for exists).

Using "get" to get it doesn't make sense if it already exists.


Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550

On 9/20/16, 12:31 PM, "R-help on behalf of Crombie, Burnette N"
<r-help-bounces at r-project.org on behalf of bcrombie at utk.edu> wrote:

>If a data.frame (r4) does not exist in my R environment, I would like 
>to create it before I move on to the next step in my script. How do I 
>make that happen?  Here is what I want to do from a code perspective:
>if (exists(r4))
>a <- 0, b <- 0, c <- 0, d <- "x", r4 <- data.frame(cbind(a,b,c,d)) }
>Thanks for your help,
>	[[alternative HTML version deleted]]
>R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see 
>PLEASE do read the posting guide
>and provide commented, minimal, self-contained, reproducible code.

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