Merging two data frames, but keeping NAs

Hi, Try ?join()

library(plyr)

y$ref <- y$id

join(x,y,by="ref")

ref id val 1   NA NA  NA 2   NA NA  NA 3   NA NA  NA 4   10 NA  NA 
5    9  9 106 6    8  8 107 7    7  7 105 8    6  6 104 9    5 NA
NA 10  NA NA  NA 11   1 NA  NA 12   2  2 101 13   3  3 102 14   4
4 103 15   5 NA  NA


A.K.


On Thursday, December 5, 2013 9:58 AM, Rainer M Krug
<Rainer at krugs.de> wrote: Hi

My brain is giving up on this...

I have the following two data.frames:

x <-  data.frame(ref=c(NA, NA, NA, 10:5, NA, 1:5)) y <-
data.frame(id = c(2, 3, 4, 6, 7, 9, 8), val = 101:107)

Which look as follow:

x

ref 1   NA 2   NA 3   NA 4   10 5    9 6    8 7    7 8    6 9    5 
10  NA 11   1 12   2 13   3 14   4 15   5

y

id val 1  2 101 2  3 102 3  4 103 4  6 104 5  7 105 6  9 106 7  8
107


Now I want to merge y into x, but that

a) the sort order of x stays the same (sort=FALSE in merge()) and 
b) the NAs stay

The result should look as follow (column id only here for
clarity):

result

ref  id  val 1   NA  NA  NA 2   NA  NA  NA 3   NA  NA  NA 4   10
NA  NA 5    9   9   106 6    8   8   107 7    7   7   105 8    6
6   104 9    5  NA  NA 10  NA  NA  NA 11   1  NA  NA 12   2   2
101 13   3   3  102 14   4   4  103 15   5  NA  NA

merge(x, y, by.x="ref", by.y="id", sort=FALSE) leaves out the NA,
but otherwise it works:

merge(x, y, by.x=1, by.y="id", sort=FALSE)

ref val 1   9 106 2   8 107 3   7 105 4   6 104 5   2 101 6   3
102 7   4 103

Is there any way that I can tell merge() to keep the NA, or how can
I achieve what I want?

Thanks,

Rainer