[R] Merging two data frames, but keeping NAs

[Rainer M Krug]

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On 12/05/13, 16:11 , Sarah Goslee wrote:
> Adding the argument all.x=TRUE to merge() will retain the NA
> values, but the only reliable way I've found to preserve order with
> NA values in a merge is to add an index column to x, merge the
> data, sort on the index column, then delete it.

Thanks Sarah - that works nicely, although it is a not so nice
workaround 0 there should be an argument in merge to keep NA...

Cheers,

Rainer

> 
> Sarah
> 
> On Thu, Dec 5, 2013 at 9:56 AM, Rainer M Krug <Rainer at krugs.de>
> wrote:
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>> 
>> 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
>> 
> 

- -- 
Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
Biology, UCT), Dipl. Phys. (Germany)

Centre of Excellence for Invasion Biology
Stellenbosch University
South Africa

Tel :       +33 - (0)9 53 10 27 44
Cell:       +33 - (0)6 85 62 59 98
Fax :       +33 - (0)9 58 10 27 44

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email:      Rainer at krugs.de

Skype:      RMkrug
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