[R] srt --- slope text with function?

[Duncan Murdoch]

On 2/5/2006 4:28 PM, ivo welch wrote:
> Dear R Wizards:  To bore everyone to death, below is an improved and
> hopefully final version of my native.slope() function.  (Thanks, Jim.)
>  In case you are not asleep yet reading yet another post of mine, may
> I ask the experts some programming questions?
> 
>   [I just saw yesterday's threat---I think it would be very, very, very nice if
>   R would remember from what files with what linenumbers code came from.
>   thus ignore below questions that mention this feature.  ALAS, I understand
>   that this cannot be done generally.  But could not function definitions at
>   least have a component that remembers this?]
> 
> * Is there a way that I can print an R functional backtrace?  Instead
> of passing my subroutine name to my function "assert()" below, it
> would be nice if I could just print the whole call tree [preferably
> with file names+line numbers] when I want my program to gracefully
> bonk out.  (PS: I think that this is also what R should print when any
> user program bonks out, not just the stop message.)  Actually, I just
> learned about traceback(), which functions nicely AFTER the program
> stops, not before.  But it gives no traceback earlier---and it does
> not give filename+lineno.

There's going to be a new section on debugging in the R 2.3.0 "Writing R 
Extensions" manual (written by Brian Ripley).  You can see it now if you 
build R-devel (or download a binary build from CRAN; I put Windows 
builds there approximately daily).  I also put together a 
Windows-oriented debugging page at 
http://www.stats.uwo.ca/faculty/murdoch/software/debuggingR/.


> 
> * is there a way to print all my user defined functions?  I have an
> init file, in which I am defining all sorts of useful utility
> functions, and I would like to print what I have defined (for memory)
> upon a read of this init file?  that is, something that has
> functionality like
>    note.all.local.definitions.now.in.vector( all.local.functions )
>    a <- function() { }
>    b <- function() { }
>    cat( all.local.functions ); # should print 'a' and 'b'.

ls.str() includes an option to select only functions.  You could also 
write your own filter for ls() output.
> 
> * is there a string variable that gives me the name of the current
> function I am in?

I don't think so, but sys.call() gets close.  Watch out though:  the 
name you see will be the name used by the caller, which may not be the 
name used when the function was written.  For example, in a function 
called from apply(), you'll see FUN, not the original name.  Objects 
don't know their own names in general, because they keep getting passed 
around.

> * SUGGESTION: can we please offer the "?:" operator ala C in addition
> to ifelse()?  This would make R code prettier.  Similarly, perl has a
> nice construct, which would be lovely, but which may not jive with the
> R syntax:
>     condition  or die("the condition", condition, "has failed");
>     condition  and cat("my condition", condition, "is met");
> I believe "or" and "and" are not defined, so this may be possible...

The ? operator is already used as a prefix and infix operator (for the 
help system), so this seems unlikely.

> * has it now become possible to embed sample data sets in R code?  (I
> asked this a while back, but there were nly kludges, no standard
> "pretty" solutions.)

I don't understand the question.  dump() produces R code that can 
reconstruct a dataset; is that what you want?
> 
> * SUGGESTION: The ?"function" docs would be terrific if they had a
> small example at the end that showed how to return multiple arguments,
> and then pick them up.  I believe this is best done through lists, but
> I am not sure.

I'd guess most people learn about functions from the Intro to R manual 
rather than the "function" man page, but this is a good suggestion.

Duncan Murdoch
> 
> I find myself programming more and more in R, so I am beginning to see
> it as my standard language, rather than as a statistical program.
> 
> Regards,
> 
> /iaw
> 
> 
> ################################################################
> #### native.slope computes a suitable srt from a function around
> #### a point on a function.  This is useful until text() gets
> #### an srt parameter that is relative to the coordinate system.
> ####   (Ideally, R would be able to slope along a function.)
> ################################################################
> 
> native.slope <- function( x, y, where.i, debug =0) {
> 
>   assert <- function( condition, routine, ... ) {
>     if (condition) return(NULL);
>     cat(paste(routine,...));
>     stop("THIS IS A FATAL ERROR!\n");
>   }
> 
>   subname= "native.slope";  # until I discover how to print a complete
> backtrace, this is it.
> 
>   assert( length(x) == length(y), subname,
> 	 "Sorry, but x and y must have equal dimensions, not ", length(x), "
> and ", length(y), "\n");
> 
>   ## try to take a symmetric field around the point to be described
>   l0= ifelse( where.i<=1, 1, where.i-1);
>   l1= ifelse( where.i>=length(y), length(y), where.i+1);
> 
>   assert( !is.na(x[l0]), subname, "Sorry, but x[",l0,"] is NaN");
>   assert( !is.na(x[l1]), subname, "Sorry, but x[",l1,"] is NaN");
>   assert( !is.na(y[l0]), subname, "Sorry, but y[",l0,"] is NaN");
>   assert( !is.na(y[l0]), subname, "Sorry, but y[",l1,"] is NaN");
> 
>   assert( y[l1] != y[l0], subname, "Sorry, but you cannot draw a slope
> on a point");
> 
>   ## native slope in a 1:1 coordinate system
>   d= ( (y[l0]-y[l1])/(x[l0]-x[l1]) );
>   if (is.na(d)) return(0); # we do not know how to handle an undefined
> spot at a function!
> 
>   ## now adjust by the axis scale and size of plot area
>   .usr <- par('usr')  # dimensions of user units
>   .plt <- par('plt') # percent of figure area that plot region is
>   d.m <- (.usr[4] - .usr[3]) / (.usr[2] - .usr[1]) * (.plt[2] -
> .plt[1]) / (.plt[4] - .plt[3])
>   assert( !is.na(d.m), subname, "Internal Error: I do not have
> sensible axis dimensions (", d.m, ")\n");
> 
>   ## now handle the drawing system
>   .fin = par('fin');
>   asp.ratio = .fin[1]/.fin[2];
>   assert( !is.na(asp.ratio), subname, "Internal Error: I do not have a
> reasonable drawing aspect ratio");
> 
>   net.slope= d/asp.ratio/d.m;
>   slope = atan(net.slope)/pi*180.0;
> 
>   if (debug) {
>     cat("\t", subname, "debug: d=", d, " (",y[where.i-1],y[where.i+1],
> x[where.i-1], x[where.i+1],")\n",
> 	"\t\td.m=",d.m, " (", .usr, ",", .plt, ")\n",
> 	"\t\tasp.ratio=", .fin, "\n\t\t==> slope=", net.slope, "=", slope, "deg\n");
>     points( x[where.i], y[where.i], pch=19 );
>   }
> 
>   return( slope = slope );
> }
> 
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