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

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Mon 06 Feb 2006 - 12:22:21 EST

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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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Mon Feb 06 12:31:07 2006

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