From Robert.McGehee at geodecapital.com  Tue Jun 29 16:46:06 2010
From: Robert.McGehee at geodecapital.com (McGehee, Robert)
Date: Tue, 29 Jun 2010 10:46:06 -0400
Subject: [Rd] POSIXlt matching bug
Message-ID: <EEBC169715EB8C438D3C9283AF0F201C08A7C74E@MSGBOSCLM2WIN.DMN1.FMR.COM>

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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[Rd] POSIXlt matching bug
McGehee, Robert