[R] Finding the last value before a certain date

[Rainer Schuermann]

dat <- structure(list(date = structure(c(14879, 14886, 14893, 14899, 
14906, 14913), class = "Date"), y = c(1356L, 1968L, 2602L, 3116L, 
3496L, 3958L)), .Names = c("date", "y"), row.names = c("1", "2", 
"3", "4", "5", "6"), class = "data.frame")

x <- as.Date( "2010-10-06" )

getY <- function( x ) { dat[ dat$date <= x, 2][ length( dat[ dat$date < x, 2] ) ] }

getY( x )
[1] 1968

getY( as.Date( "2010-10-17" ) )
[1] 2602

Is that what you want?

Rgds,
Rainer


-------- Original-Nachricht --------
> Datum: Thu, 19 Jul 2012 09:42:05 +0200
> Von: Robert Latest <boblatest at gmail.com>
> An: > Betreff: [R] Finding the last value before a certain date

> Hello all,
> 
> I have a dataframe that looks like this:
> 
> head(df)
>         date    y
> 1 2010-09-27 1356
> 2 2010-10-04 1968
> 3 2010-10-11 2602
> 4 2010-10-17 3116
> 5 2010-10-24 3496
> 6 2010-10-31 3958
> 
> I need a function that, given any date, returns the y value
> corresponding to the given date or the last day before the given date.
> 
> Example:
> 
> Input: as.Date("2010-10-06"). Output: 1968 (because the last value is
> from 2010-10-04)
> 
> I've been tinkering with this for an hour now, without success. I
> think the solution is either surprisingly complicated or surprisingly
> simple.
> 
> Thanks,
> robert
> 
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