[R] Error

[William Dunlap]

You can debug this sort of thing yourself by altering
your function to tell you what its inputs are when
things go wrong.  E.g., change your original
  foo <- function(x) {
       unlist(lapply(x, FUN = function(z) cumsum(z) - z))
  }
to
  foo <- function(x) {
       retval <- unlist(lapply(x, FUN=function(z), cumsum(z) - z))
       if (length(retval)==0)) {
           cat("foo: length(retval)==0 when x=\n")
           str(x)
           stop("problem in foo")
       }
       retval
  }
For a more general solution, try setting options("error") to one of
the debugging error handlers.  options(error=recover)
works but there are others.  It takes a little while
to figure out how to use the error handler but once
you do you can solve your own problems.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of 
> rex.dwyer at syngenta.com
> Sent: Monday, February 28, 2011 9:31 AM
> To: murdoch.duncan at gmail.com; mathijsdevaan at gmail.com
> Cc: r-help at r-project.org
> Subject: Re: [R] Error
> 
> I have to agree that it's pretty hard to take something that 
> works and figure out why it doesn't work :)
> The only other suggestion is that sometimes I find that this 
> sort of error goes away if I add "drop=FALSE" to the 
> subsetting, and, if so,  that usually lets me figure out why.
> 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Duncan Murdoch
> Sent: Sunday, February 27, 2011 5:52 AM
> To: mathijsdevaan
> Cc: r-help at r-project.org
> Subject: Re: [R] Error
> 
> On 11-02-26 8:26 AM, mathijsdevaan wrote:
> > Mean doesn't work either... I understand that the message 
> "replacement has 0
> > items, need 37597770" implies that the function is not 
> returning any values,
> > but I don't understand why then this is not the case in the example.
> >
> > DF = data.frame(read.table(textConnection("    A  B  C  D  E
> > 1 1  a  1999  1  0
> > 2 1  b  1999  0  1
> > 3 1  c  1999  0  1
> > 4 1  d  1999  1  0
> > 5 2  c  2001  1  0
> > 6 2  d  2001  0  1
> > 7 3  a  2004  0  1
> > 8 3  b  2004  0  1
> > 9 3  d  2004  0  1
> > 10 4  b  2001  1  0
> > 11 4  c  2001  1  0
> > 12 4  d  2001  0  1"),head=TRUE,stringsAsFactors=FALSE))
> >
> > DF = DF[order(DF$B,DF$C),]
> >
> > #first option - works fine in example and my target data frame
> > DF$F = ave(DF$D,DF$B, FUN = function(x) cumsum(x)-x)
> > DF$G = ave(DF$E,DF$B, FUN = function(x) cumsum(x)-x)
> >
> > #second option - works fine in example but not in my target 
> data frame
> > foo<- function(x)
> >       {
> >       unlist(lapply(x, FUN = function(z) cumsum(z) - z))
> >       }
> > n<-ave(DF[,c(4:5)],DF$B,FUN = foo)
> >
> > Why is this second option not working in my target data 
> frame (which is much
> > bigger than the example)?
> 
> Presumably something is different about it.  I don't see how 
> you expect
> people to debug your problem when you don't show it.
> 
> If you want help, you need to give us an example that shows the error.
> Start with your large dataset, and shrink it as much as possible, but
> not so much that the error goes away.  (I suspect when you do this,
> you'll end up seeing your error yourself.  But maybe not.)
> 
> Duncan Murdoch
> 
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