[R] Date Time Conversion problems...

[Dirk Eddelbuettel]

On Wed, Feb 04, 2004 at 08:31:56AM -0600, Shawn Way wrote:
> At one time (version 1.7), the code below used to work for converting and
> extracting based on the Date Time.  In version 1.8.1, something changed I
> know, but I cannot for the life of me figure out what...
> 
> Data:
> 
> UserName,RequestDate,PO,OrderDate,ExpDelivDate,Vendor,Total
> "Woody, Jim",12/19/2002,AP15063,1/7/2003,2/10/2003,Ames ,8570
> "Harrold, Paul",12/31/2002,AP15083,1/9/2003,1/10/2003,Ryan ,1039.5
> "Vo, Hoang",12/27/2002,AP15055,1/6/2003,1/13/2003,TIDEA,1005.36
> "Way, Shawn",1/2/2003,AP15043,1/2/2003,1/9/2003,JS   ,1000
> "Vo, Hoang",1/7/2003,SO17440,1/8/2003,12/31/2003,USFi-,3705
> "Harrold, Paul",1/10/2003,AP15122,1/13/2003,1/14/2003,FishM,65.06
> 
> Old Code:
> 
> library(lattice)
> data <- read.csv("h:\\list3.csv",header=TRUE)
> data2 <-
> data.frame(Name=data$UserName,Date=data$RequestDate,Vendor=data$Vendor,Cost=
> data$Total)
> data2$Date <- strptime(as.character(data2$Date),format="%m/%d/%Y")
> start <- strptime(c("1/01/2003"),format="%m/%d/%Y")
> end <- strptime(c("12/31/2003"),format="%m/%d/%Y")
> data3 <- data2[data2$Date >= start & data2$Date <= end,]
> lset(col.whitebg())
> xyplot(Cost~as.POSIXct(Date)|Name,data=data3,
>        xlab="Date",
>        ylab="PO Cost($)",
>        ylim=c(0,10000),
>        panel= function(x,y){
>          a <- mean(y)
>          panel.grid(h=-1,v=2)
>          panel.xyplot(x,y)
>          panel.abline(h=a,col="red")
>        }
>        )
> 
> The error I get is from line 4, 
> 
> > data2$Date <- strptime(as.character(data2$Date),format="%m/%d/%Y")
> Error in "$<-.data.frame"(`*tmp*`, "Date", value =
> strptime(as.character(data2$Date),  : 
> 	replacement has 9 rows, data has 230

The '9 rows' gives it aways -- it works with an explicit time object cast:

data2$Date <- as.POSIXct(strptime(as.character(data2$Date),format="%m/%d/%Y"))
start <- as.POSIXct(strptime(c("1/01/2003"),format="%m/%d/%Y"))
end <- as.POSIXct(strptime(c("12/31/2003"),format="%m/%d/%Y"))

> This used to work for replacing the dates with POSIX values...
> 
> Also of interest is the extraction for data3, is this the correct method for
> extraction?

It works.  A more formal way is in the subsetting and range functions for
the its package.

Dirk

-- 
The relationship between the computed price and reality is as yet unknown.  
                                             -- From the pac(8) manual page