From: Erik Iverson <iverson_at_biostat.wisc.edu>

Date: Tue, 03 Jun 2008 21:09:23 -0500

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 - 02:12:56 GMT

Date: Tue, 03 Jun 2008 21:09:23 -0500

Alan -

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 ####
*

When learning R, you have the power of the interpreter at all times. You have defined x and y above to be numeric vectors of length 7 each. Try typign x - y at the interpreter, and you'll see you get another numeric vector of length 7. Now try (x - y) >= 0 , and you'll get a logical vector of length 7. However, if does not want a logical vector of length 7, it wants a logical vector of length 1, see the 'cond' argument of ?if. However, the ifelse function should do what you want, see ?ifelse.

Here's an example using it

folds2 <- function(x, y) {

ifelse(x - y >= 0, 2^(x - y), -(2^abs(x - y))) }

folds2(x, y) should give you your answer...

*>
*

> ## 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
*

Same idea as above here...

> ################################################################################

*> #### 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)
**> #################
*

I'm not exactly sure what you'd like here, but hopefully with the above you can figure it out. Let me know if you have any questions!

Best,

Erik Iverson

*>
*

> Thank you,

*> Alan
**>
**> P.S. why does ?function not work
*

What do you expect it to do? It shows the help page for 'function' here.

*>
**> ______________________________________________
**> 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.

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 - 02:12:56 GMT

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