[R] NA problem when use paste function

[Lu, Jiang]

Dear R helpers,

I was doing a genetic project with two datasets X and Y. There are
some IDs in both data sets, and others in either data set. I used
"merge(x,y,by="ID",all=TRUE)". The data set Y contains a variable (a
genotype) which is also in data X. When I merge X with Y, these two
variables were automatically re-named by appending .x and .y to the
original variable names. As you can see on the following list, I would
like to take whatever available (non-missing non-NA) in X or Y as the
final value for the genotype S3Allel1. I used paste() function.
However, it converts <NA> to NA as character. Would you please tell me
how I can just get the genotype without pasting the NA to it? I
checked the document of paste() and noticed that it used
as.character() to the vector argument. I guess that is the reason I
got "NA" as a string for the new variable I created (S3Allele1).
Should I use any other funtion to avoid this problem? Any insight is
appreciated!

           ID      S3Allele1.x S3Allele1.y S3Allele1
1       10003           G        <NA>      G NA
2       10004           A        <NA>      A NA
3       10005           A        <NA>      A NA
4       10006           A        <NA>      A NA
5       10007           G        <NA>      G NA
6       10008           A        <NA>      A NA
7       10009           A        <NA>      A NA
8       10010           A        <NA>      A NA
9       10011           A        <NA>      A NA
10      10013           A        <NA>      A NA
11      10014           A        <NA>      A NA
12      10015           A        <NA>      A NA
13      10016           A        <NA>      A NA
14      10017           A        <NA>      A NA
15      10018           A        <NA>      A NA
16      10019           G        <NA>      G NA
17      10020           A        <NA>      A NA
18      10021           G        <NA>      G NA
19      10022           A        <NA>      A NA
20      10023           G        <NA>      G NA
21      10024           G        <NA>      G NA
22      10025           G        <NA>      G NA
23      10027           G        <NA>      G NA
24      10028           G        <NA>      G NA
25      10029           G        <NA>      G NA
26      10031           G        <NA>      G NA
27      10032           A        <NA>      A NA
28      10033        <NA>                   NA
29      10035           A        <NA>      A NA
30      10037           A        <NA>      A NA
31      10038        <NA>           A      NA A
32      10039        <NA>           A      NA A