[R] merging 2 frames while keeping all the entries from the "reference" frame

[Gabor Grothendieck]

On Mon, Apr 4, 2011 at 1:09 PM, Dimitri Liakhovitski
<dimitri.liakhovitski at gmail.com> wrote:
> Hello!
> I have my data frame "mydata" (below) and data frame "reference" -
> that contains all the dates I would like to be present in the final
> data frame.
> I am trying to merge them so that the the result data frame contains
> all 8 dates in both subgroups (i.e., Group1 should have 8 rows and
> Group2 too). But when I merge it it's not coming out this way. Any
> hint would be greatly appreciated!
> Dimitri
>
> mydata<-data.frame(mydate=rep(seq(as.Date("2008-12-29"), length = 8,
> by = "week"),2),
> group=c(rep("Group1",8),rep("Group2",8)),values=rnorm(16,1,1))
> (reference);(mydata)
> set.seed(1234)
> out<-sample(1:16,5,replace=F)
> mydata<-mydata[-out,]; dim(mydata)
> (mydata)
>
> # "reference" contains the dates I want to be present in the final data frame:
> reference<-data.frame(mydate=seq(as.Date("2008-12-29"), length = 8, by
> = "week"))
>
> # Merging:
> new.data<-merge(mydata,reference,by="mydate",all.x=T,all.y=T)
> new.data<-new.data[order(new.data$group,new.data$mydate),]
> (new.data)
> # my new.data contains only 7 rows in Group 1 and 4 rows in Group 2
>

It might make more sense to put each group into its own column since
then the object is a multivariate time series:

> library(zoo)
> z <- merge(read.zoo(mydata, split = 2), zoo(, reference[[1]]), all = c(FALSE, TRUE))
> z
              Group1    Group2
2008-12-29 2.0266215        NA
2009-01-05        NA        NA
2009-01-12 1.0255344        NA
2009-01-19 1.3880938 0.8135788
2009-01-26 1.4380978 1.6068682
2009-02-02 1.1764965        NA
2009-02-09 1.1578531 1.4484447
2009-02-16 0.6673568 1.4760864

although if you really need to you could string them out like this:

library(reshape2)
melt(data.frame(time(z), coredata(z)), id = 1)

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com