[Rd] Strict seq: a recommendation

[Tony Plate]

The way I avoid this problem is to use seq(len=n) instead of 1:n.
Of course, the syntax can get inconvenient for starting values other 
than 1 or 0, but I haven't found that to be much of a problem.

Using the idiom 1:n in programming (as opposed to interactive use) 
results in errors commonly enough that it probably wouldn't be a bad 
idea for quality control tools to warn about contructs like 'for (* in 
*:*)' .

BTW, it would probably be nice for a seqStrict() function to return a 
vector of the same storage mode as seq(), e.g.:

 > storage.mode(seq(len=0))
[1] "integer"
 > storage.mode(1:3)
[1] "integer"
 > n <- 3
 > storage.mode(n)
[1] "double"
 > storage.mode(1:n)
[1] "integer"
 > storage.mode(c())
[1] "NULL"
 >

-- Tony Plate

Dominick Samperi wrote:
> In for loops of the form:
> for(m in seq(beg,end))
> ...
> 
> when beg > end, the default behavior is
> to decrement, and the action described
> by ... is executed at least once.
> 
> On the other hand, if you view this
> construction as a translation of the C code:
> for(m = beg; m < end; m++)
> ...
> 
> then the semantics of C/C++ is not
> respected, because the code in ... is
> not executed when beg > end in
> the case of C/C++.
> 
> To get the proper C/C++ semantics I
> use the following replacement for seq:
> 
> seqStrict <- function(beg, end, step=1) {
>   if((beg >= end && step > 0) || (beg <= end && step < 0))
>     val <- c() # null vector
>   else
>     val <- seq(beg,end,step)
>   val
> }
> 
> Perhaps it would be useful to add an option to
> seq, so seq(beg,end,strict=TRUE) amounts to
> the same thing as using seqStrict(beg,end).
> 
> ds
> 
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