[R] Lost in POSIX

[David Winsemius]

On Nov 21, 2010, at 3:52 PM, Dimitri Shvorob wrote:

>
> Can someone please fix this snippet? (i.e. append to the dataframe a  
> column
> containing "truncated" time value)?
>
> df = structure(list(t = structure(c(1033963406.044, 1033974144.847,
> 1033988418.836), class = c("POSIXt", "POSIXct"))), .Names = "t",  
> row.names =
> c(NA,
> 3L), class = "data.frame")

 > df
                     t
1 2002-10-07 00:03:26
2 2002-10-07 03:02:24
3 2002-10-07 07:00:18
 > df$dt <- as.Date(df$t)
 > df
                     t         dt
1 2002-10-07 00:03:26 2002-10-07
2 2002-10-07 03:02:24 2002-10-07
3 2002-10-07 07:00:18 2002-10-07

>
> # Try 1
> df$day = trunc.POSIXt(as.POSIXlt(df$t, origin =  "1970-01-01"),  
> units =
> "day")
>
> Error in `$<-.data.frame`(`*tmp*`, "day", value = list(0, 0L, 0L,  
> 7L,  :
>  replacement has 9 rows, data has 3
>
> # Try 2
> f = function(t) trunc.POSIXt(as.POSIXlt(t, origin =  "1970-01-01"),  
> units =
> "day")
> df$day  = sapply(df$t, f)
>
> Error in `$<-.data.frame`(`*tmp*`, "day", value = list(sec = 0, min  
> = 0L,  :
>  replacement has 9 rows, data has 3
>
> -- 
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>
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David Winsemius, MD
West Hartford, CT