From pburns at pburns.seanet.com  Fri Jul 22 15:43:28 2005
From: pburns at pburns.seanet.com (Patrick Burns)
Date: Fri, 22 Jul 2005 14:43:28 +0100
Subject: [Rd] [R] sequence()
In-Reply-To: <Pine.LNX.4.61.0507221011100.28301@gannet.stats>
References: <7CBD9E72-0812-47A5-8803-34FFDAB37274@soc.soton.ac.uk>
	<Pine.LNX.4.61.0507221011100.28301@gannet.stats>
Message-ID: <42E0F800.1050002@pburns.seanet.com>

I definitely agree that 'sequence' is not the right name
for this functionality.  The functionality is occasionally
useful -- I've been asked for it several times. But I do
wonder if it is basic enough that it should be in 'base'.

The function could be rewritten to create the proper
length of the answer at the outset since that is known.
It could then be used as an example (somewhere) of
how not to fragment memory.

Patrick Burns
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Prof Brian Ripley wrote:

>R-help is not the list for R development questions: you didn't want help 
>did you? --> moved to R-devel.
>
>I do wonder why
>
>  
>
>>sequence(c(0,-1))
>>    
>>
>[1]  1  0  1  0 -1
>
>is considered useful.
>
>Given that the definition seems flawed and I could not find any uses of 
>this function in any package my reaction was to suggest the function be 
>deprecated on the way to removal.  (I also do not understand why anyone 
>would expect sequence() to do that and not one of the many things which 
>seq() does.)
>
>We certainly do not want to replace a function that works as described at 
>a reasonable speed by one that does not work as described, however fast.
>
> 	`Accuracy first, speed second'.
>
>
>On Fri, 22 Jul 2005, Robin Hankin wrote:
>
>  
>
>>Function sequence() repeatedly concatenates
>>its output, and this is slow.
>>    
>>
>
>  
>
>>It is possible to improve on the performance of sequence by
>>defining
>>
>> myseq <- function(x){unlist(sapply(x,function(i){1:i}))}
>>    
>>
>
>I don't think you want sapply here, but lapply.  Try
>
>  
>
>>myseq(c(2,2))
>>    
>>
>      [,1] [,2]
>[1,]    1    1
>[2,]    2    2
>
>sic!
>
>  
>
>>The following session compares the  performance of
>>myseq(), and sequence(), at least on my G5:
>>
>>
>>    
>>
>>>identical(sequence(1:50),myseq(1:50))
>>>      
>>>
>>[1] TRUE
>>    
>>
>>>system.time(ignore <- sequence(1:800))
>>>      
>>>
>>[1] 1.16 0.88 2.07 0.00 0.00
>>    
>>
>>>system.time(ignore <- sequence(1:800))
>>>      
>>>
>>[1] 1.14 0.84 1.99 0.00 0.00
>>    
>>
>>>system.time(ignore <- myseq(1:800))
>>>      
>>>
>>[1] 0.02 0.02 0.04 0.00 0.00
>>    
>>
>>>system.time(ignore <- myseq(1:800))
>>>      
>>>
>>[1] 0.03 0.00 0.03 0.00 0.00
>>    
>>
>>(the time differential is even more marked for longer arguments).
>>    
>>
>
>and much less for more realistic shorter arguments.
>
>  
>
>>Is there any reason why we couldn't use  this definition instead?
>>    
>>
>
>The fact that it sometimes gives the wrong answer, for one.
>
>  
>



[Rd] [R] sequence()
Patrick Burns