[R] The opposite of "lag"

[Dimitri Liakhovitski]

Basically, if you look at the A lagged below, then you see how in each
group the values of A "move" downwards": and NA is added on top and
the last value in each group disappears.
I am trying to get the opposite: the first value in each group
disappears and NA is added at the bottom.
D.

set.seed(1234)
A <- data.frame(year=rep(c(1980:1984),3), group=
factor(sort(rep(1:3,5))), DV=c(rnorm(15)))
lag.it <- function(x) {
  DV <- ts(x$DV, start = x$year[1])
	idx <- seq(length = length(DV))
	DVs <- cbind(DV, lag(DV, -1))[idx,]
	out<-cbind(x, DVs[,2])  # wages[,2]
   names(out)[length(out)]<-"DV.lag"
   return(out)
}
A
A.lagged <- do.call("rbind", by(A, A$group, lag.it))
A.lagged





On Wed, Jul 21, 2010 at 12:18 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Sorry, I don't think it's working.
> the last 3 columns (on the right) of result contain the original data
> of each group.
> But there is no shift at all. I am trying to reach the following
> result for each group: The first number disappears and at the bottom
> an NA appears.
> Is it possible?
>
> On Wed, Jul 21, 2010 at 12:12 PM, Dimitri Liakhovitski
> <dimitri.liakhovitski at gmail.com> wrote:
>> Never mind- I figured it out:
>>
>> A
>> library(zoo)
>> z <- read.zoo(A, index = 1, split = "group", frequency = 1)
>> z <- as.zooreg(z) ###
>> result<-lag(z, c(-1, 0, 1))
>> A
>> result
>>
>> Thank you very much!
>>
>> On Wed, Jul 21, 2010 at 12:08 PM, Dimitri Liakhovitski
>> <dimitri.liakhovitski at gmail.com> wrote:
>>> Thank you, Gabor, but sorry - what is the exact order of those rows again?
>>> Thank you!
>>> Dimitri
>>>
>>> On Wed, Jul 21, 2010 at 11:59 AM, Gabor Grothendieck
>>> <ggrothendieck at gmail.com> wrote:
>>>> On Wed, Jul 21, 2010 at 10:50 AM, Gabor Grothendieck
>>>> <ggrothendieck at gmail.com> wrote:
>>>>> On Wed, Jul 21, 2010 at 10:14 AM, Dimitri Liakhovitski
>>>>> <dimitri.liakhovitski at gmail.com> wrote:
>>>>>> Hello!
>>>>>>
>>>>>> I have a data frame A (below) with a grouping factor (group). I take
>>>>>> my DV and create the new, lagged DV by applying the function lag.it
>>>>>> (below). It works fine.
>>>>>>
>>>>>> A <- data.frame(year=rep(c(1980:1984),3), group=
>>>>>> factor(sort(rep(1:3,5))), DV=c(rnorm(15)))
>>>>>> lag.it <- function(x) {
>>>>>>  DV <- ts(x$DV, start = x$year[1])
>>>>>>  idx <- seq(length = length(DV))
>>>>>>  DVs <- cbind(DV, lag(DV, -1))[idx,]
>>>>>>  out<-cbind(x, DVs[,2])  # wages[,2]
>>>>>>   names(out)[length(out)]<-"DV.lag"
>>>>>>   return(out)
>>>>>> }
>>>>>> A
>>>>>> A.lagged <- do.call("rbind", by(A, A$group, lag.it))
>>>>>> A.lagged
>>>>>>
>>>>>>
>>>>>> Now, I am trying to create the oppostive of lag for DV (should I call
>>>>>> it "lead"?)
>>>>>> I tried exactly the same as above, but with a different number under
>>>>>> lag function (below), but it's not working. I am clearly doing
>>>>>> something wrong. Any advice?
>>>>>> Thanks a lot!
>>>>>>
>>>>>>
>>>>>> lead.it <- function(x) {
>>>>>>  DV <- ts(x$DV, start = x$year[1])
>>>>>>  idx <- seq(length = length(DV))
>>>>>>  DVs <- cbind(DV, lag(DV, 2))[idx,]
>>>>>>  out<-cbind(x, DVs[,2])
>>>>>>   names(out)[length(out)]<-"DV.lead"
>>>>>>   return(out)
>>>>>> }
>>>>>> A
>>>>>> A.lead <- do.call("rbind", by(A, A$group, lead.it))
>>>>>> A.lead
>>>>>>
>>>>>
>>>>> Try this:
>>>>>
>>>>> library(zoo)
>>>>> z <- read.zoo(A, index = 1, split = "group", frequency = 1)
>>>>> lag(z, c(-1, 0, 1))
>>>>>
>>>>
>>>> The ### line was missing:
>>>>
>>>> library(zoo)
>>>> z <- read.zoo(A, index = 1, split = "group", frequency = 1)
>>>> z <- as.zooreg(z) ###
>>>> lag(z, c(-1, 0, 1))
>>>>
>>>
>>>
>>>
>>> --
>>> Dimitri Liakhovitski
>>> Ninah Consulting
>>> www.ninah.com
>>>
>>
>>
>>
>> --
>> Dimitri Liakhovitski
>> Ninah Consulting
>> www.ninah.com
>>
>
>
>
> --
> Dimitri Liakhovitski
> Ninah Consulting
> www.ninah.com
>



-- 
Dimitri Liakhovitski
Ninah Consulting
www.ninah.com