Thanks for the answers from Duncan, Bill, Gabor, and Henrik. You
convinced me that
1. The solution
if (x > 1){
for (x in 2:x){
...
is the easiest, most effective, and most easy-to-understand.
2. However, Bill (and Henrik) raised the question of replacing '1' with
'1L'; I understand the meaning of that, but does it matter (in practice)?
3. Noone commented upon
i <- 1
while (i < x){
i <- i + 1
...
}
I suppose that it means that it is the best solution.
Thanks, and Happy New Year 2014!
Göran
On 12/22/2013 06:57 PM, William Dunlap wrote:
for (i in seq_len(x - 1) + 1)
should be efficient and safe.
Oops, not safe when x is 0.
Also, the '+ 1' should be '+ 1L' to get the same answer as
seq_len(x)[-1].
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf
Of Duncan Murdoch
Sent: Saturday, December 21, 2013 3:52 PM
To: Göran Broström; R-help@r-project.org
Subject: Re: [R] seq_len and loops
On 13-12-21 6:50 PM, Duncan Murdoch wrote:
On 13-12-21 5:57 PM, Göran Broström wrote:
I was recently reminded on this list that
"Using 1:ncol() is bad practice (seq_len is designed for that purpose)"
(Ripley)
This triggers the following question: What is "good practice" for
2:ncol(x)? (This is not a joke; in a recursive situation it often makes
sense to perform the calculation for the start value i = 1, then
continue with a loop over the rest, "the Fortran way";)
I usually use
if (ncol(x) > 1)
for (i in 2:ncol(x)){
....
but I can think of
for (i in seq_len(x - 1)){
I <- i + 1
....
and
i <- 1
while (i < ncol(x)){
i <- i + 1
....
What is "good practice" (efficient and safe)?
for (i in seq_len(x - 1) + 1)
should be efficient and safe.
Oops, not safe when x is 0.
>
A little less efficient, but clearer would be
for (i in seq_len(x)[-1])
Duncan Murdoch
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