From: Simon Blomberg <s.blomberg1_at_uq.edu.au>

Date: Wed, 04 Jun 2008 12:07:16 +1000

Date: Wed, 04 Jun 2008 12:07:16 +1000

Use ifelse() rather than if () {} else {}. It's vectorized and very useful for applying to elements along vectors. The latter idiom is much better for control of flow in programs and functions.

folds <- function (x, y) ifelse(x-y >= 0, 2^(x-y), -(2^abs(x-y)))

z <- folds(x, y)

*> z
*

[1] 16 1 4 4 -4 4 -256

*>
*

?function works for me. Here's my setup:

R version 2.7.0 (2008-04-22)

x86_64-pc-linux-gnu

Cheers,

Simon.

On Tue, 2008-06-03 at 20:47 -0500, ALAN SMITH wrote:

*> Hello R users and developers,
**> I am trying to write several functions (fairly new at this) in order
**> to avoid using loops on large data frames (because they are slow). I
**> wrote the function below and it seems to get hung on the first part of
**> the if statement and then applies that condition to rest of the
**> function. So if (x-y) is greater than 0 the function uses the true
**> statement for the calculations. Could someone please offer some
**> advise on how to write these functions a little better or a type
**> "apply" that I may use with two (or more) different vectors of data
**> required by a single functions.
**> ####################### Examples
**> #######################################################
**> ## example 1 ###
**> x<-c(5,6,4,3,5,3,1)
**> y<-c(1,6,2,1,7,1,9)
**> folds<-function(x,y) (if((x-y)>=0) {2^(x-y)} else{-(2^abs(x-y))})
**> z<-folds(x,y)
**> check<-cbind(x,y,z)
**> View(check)
**>
**> Warning message:
**> In if ((x - y) >= 0) { :
*

> the condition has length > 1 and only the first element will be used

*> ### why will it only use the first element and how to I get around
**> this ####
**>
**> ## example 2 making the fist comparison negative ###
**> x1<-c(5,6,4,3,5,3,1)
**> y1<-c(11,6,2,1,7,1,9)
**> folds<-function(x,y) (if((x-y)>=0) {2^(x-y)} else{-(2^abs(x-y))})
**> z1<-folds(x1,y1)
**> check2<-cbind(x1,y1,z1)
**> View(check2)
**> Warning message:
**> In if ((x - y) >= 0) { :
**> the condition has length > 1 and only the first element will be used
**> ################################################################################
**> #### loop I am trying to avoid writing many many times #####
**> folds2<-NULL
**> xy<-as.data.frame(cbind(x,y))
**> for (i in 1:nrow(xy)) {
**> diff<-xy$x[i]-xy$y[i]
**> folds2[i]<-if(diff>=0) {2^diff} else{-(2^abs(diff))}
**> }
**> xyz<-cbind(xy,folds2)
**> View(xyz)
**> #################
**>
**> Thank you,
**> Alan
**>
**> P.S. why does ?function not work
**>
**> ______________________________________________
**> 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.
*

-- Simon Blomberg, BSc (Hons), PhD, MAppStat. Lecturer and Consultant Statistician Faculty of Biological and Chemical Sciences The University of Queensland St. Lucia Queensland 4072 Australia Room 320 Goddard Building (8) T: +61 7 3365 2506 http://www.uq.edu.au/~uqsblomb email: S.Blomberg1_at_uq.edu.au Policies: 1. I will NOT analyse your data for you. 2. Your deadline is your problem. The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. - John Tukey. ______________________________________________ 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.Received on Wed 04 Jun 2008 - 02:10:11 GMT

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