[Rd] [R] Subscripting a matrix-like object

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Jeffrey J. Hallman
> Sent: Friday, May 14, 2010 9:17 AM
> To: r-help at stat.math.ethz.ch
> Subject: Re: [R] Subscripting a matrix-like object
> 
> jhallman at frb.gov writes:
> 
> Answering my own question here, so you can ignore this unless you are
> really interested in some fairly obscure stuff.  It turns out 
> that this works:
> 
> singleIndex <- missing(j) && (length(sys.call()) == 
> length(match.call()))
> 
> since sys.call() has an element for the empty argument created by
> 
> x[i,] <- value
> 
> and match.call() does not.  But it is pretty obscure.

I was curious about this because in the version of R
I'm using (2.11.0, 2010-04-22), nargs() does distinguish
between x[i] and x[i,].  E.g., with the following
replacement function
  `[<-.foo` <- function (x, i, j, ..., value)
  {
      cat("[<-.foo: nargs=", nargs(), "\n", sep = "")
      cat("         sys.call()=", deparse(sys.call()), "\n", sep = "")
      cat("         missing(i)=", missing(i), "\n", sep = "")
      cat("         missing(j)=", missing(j), "\n", sep = "")
      x
  }
I get
  > fooObject <- structure(1:4, class="foo")
  > fooObject[1] <- 12
  [<-.foo: nargs=3
           sys.call()=`[<-.foo`(`*tmp*`, 1, value = 12)
           missing(i)=FALSE
           missing(j)=TRUE
  > fooObject[1,] <- 12
  [<-.foo: nargs=4
           sys.call()=`[<-.foo`(`*tmp*`, 1, , value = 12)
           missing(i)=FALSE
           missing(j)=TRUE
  > fooObject[,1] <- 12
  [<-.foo: nargs=4
           sys.call()=`[<-.foo`(`*tmp*`, , 1, value = 12)
           missing(i)=TRUE
           missing(j)=FALSE
  
Is this a bug in nargs() that was recently fixed?

sys.call() and especially match.call() are
fairly expensive functions to call so it would be nice
to be able to avoid them.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  

> 
> Jeff
> 
> > I have an S3 class called "tis" (Time Indexed Series) which 
> may or may
> > not have multiple columns.  I have a function "[<-.tis" that I've
> > reproduced below.  
> >
> > My question is this: inside of "[<-.tis", how can I 
> distinguish between
> > calls of the form 
> >
> > x[i] <- someValue
> >
> > and
> >
> > x[i,] <- someValue ?
> >
> > In either case, nargs() is 3, and looking at the values 
> from sys.call()
> > and match.call() I could not tell them apart.  Am I missing 
> something?
> >
> >
> > "[<-.tis" <- function(x, i, j, ..., value){
> >   tif <- tif(x)
> >   xStart <- start(x)
> >   x <- stripTis(x)
> >   if(missing(i)){
> >     if(missing(j)) x[]   <- value
> >     else           x[,j] <- value
> >   }
> >   else {
> >     i <- i[!is.na(i)]
> >     if(is.numeric(i)){
> >       if(!is.ti(i) && couldBeTi(i, tif = tif))
> >         i <- asTi(i)
> >       if(is.ti(i)){
> >         i <- i + 1 - xStart
> >         if(any(i < 1)){
> >           newRows <- 1 - min(i)
> >           xStart <- xStart - newRows
> >           if(is.null(m <- ncol(x)))  m <- 1
> >           i <- i + newRows
> >           if(is.matrix(x))
> >             x <- rbind(matrix(NA, newRows, m), x)
> >           else
> >             x <- c(rep(NA, newRows), x)
> >         }
> >       }
> >     }
> >     else if(!is.logical(i)) stop("non-numeric, non-logical 
> row index")
> >    if(is.matrix(x)){
> >       if(any(i > nrow(x))){
> >         newRows <- max(i) - nrow(x)
> >         x <- rbind(x, matrix(NA, newRows, ncol(x)))
> >       }
> >       if(missing(j)){
> >         if(is.matrix(i))  x[i] <- value
> >         else {
> >           if(is.logical(i))
> >             x[i,] <- rep(value, length = sum(i)*ncol(x))
> >           else
> >             x[i,] <- rep(value, length = length(i)*ncol(x))
> >         }
> >       }
> >       else x[i,j] <- value
> >     }
> >     else x[i] <- value
> >   }
> >   start(x) <- xStart
> >   class(x) <- c("tis", oldClass(x))
> >   x
> > }
> >
> 
> -- 
> Jeff
> 
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