[Rd] POSIXlt matching bug

[Sklyar, Oleg (London)]

POSIXlt is a list and it is not a list of dates or times, it is a list
of 

> x <- as.POSIXlt(Sys.Date())
> names(x)
[1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"
"isdst"

So if you want to match these things, you should use POSIXct or any
other numeric-based format (as POSIXct is just a double value for the
number of seconds since 1970-01-01) e.g.

> z <- as.POSIXct(Sys.Date())
> x <- as.POSIXct(Sys.Date())
> z==x
[1] TRUE
> match(z,x)
[1] 1
> z %in% x
[1] TRUE

Dr Oleg Sklyar
Research Technologist
AHL / Man Investments Ltd
+44 (0)20 7144 3803
osklyar at maninvestments.com 

> -----Original Message-----
> From: r-devel-bounces at r-project.org 
> [mailto:r-devel-bounces at r-project.org] On Behalf Of McGehee, Robert
> Sent: 29 June 2010 15:46
> To: R-bugs at r-project.org; r-devel at r-project.org
> Subject: [Rd] POSIXlt matching bug
> 
> I came across the below mis-feature/bug using match with 
> POSIXlt objects
> (from strptime) in R 2.11.1 (though this appears to be an old issue).
> 
> > x <- as.POSIXlt(Sys.Date())
> > table <- as.POSIXlt(Sys.Date()+0:5)
> > length(x)
> [1] 1
> > x %in% table  # I expect TRUE
> [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
> > match(x, table) # I expect 1
> [1] NA NA NA NA NA NA NA NA NA
> 
> This behavior seemed more plausible when the length of a 
> POSIXlt object
> was 9 (back in the day), however since the length was redefined, the
> length of x no longer matches the length of the match function output,
> as specified by the ?match documentation: "A vector of the same length
> as 'x'".
> 
> I would normally suggest that we add a POSIXlt method for match that
> converts x into POSIXct or character first. However, match does not
> appear to be generic. Below is a possible rewrite of match 
> that appears
> to work as desired.
> 
> match <- function(x, table, nomatch = NA_integer_, 
> incomparables = NULL)
> 
>     .Internal(match(if(is.factor(x)||inherits(x, "POSIXlt"))
> as.character(x) else x,
>                     if(is.factor(table)||inherits(table, "POSIXlt"))
> as.character(table) else table,
>                     nomatch, incomparables))
> 
> That said, I understand some people may be very sensitive to the speed
> of the match function, and may prefer a simple change to the ?match
> documentation noting this (odd) behavior for POSIXlt. 
> 
> Thanks, Robert
> 
> R.version
>                _                            
> platform       x86_64-unknown-linux-gnu     
> arch           x86_64                       
> os             linux-gnu                    
> system         x86_64, linux-gnu            
> status                                      
> major          2                            
> minor          11.1                         
> year           2010                         
> month          05                           
> day            31                           
> svn rev        52157                        
> language       R                            
> version.string R version 2.11.1 (2010-05-31)
> 
> Robert McGehee, CFA
> Geode Capital Management, LLC
> One Post Office Square, 28th Floor | Boston, MA | 02109
> Tel: 617/392-8396    Fax:617/476-6389
> mailto:robert.mcgehee at geodecapital.com
> 
> 
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