[R] merging/intersecting 2 data frames

[Erin Hodgess]

Dear R People:

I have two data frames, a.df and b.df as seen here:

> a.df[1:10,]
        DATE GENDER PATIENT_ID AGE             SYNDROME
1  4/16/2009      F      23686  45         RASH ON BODY
2  4/16/2009      F      13840  35         CANT URINATE
3  4/16/2009      M      12895  30       BLURRED VISION
4  4/16/2009      M      18375  33       UNABLE TO VOID
5  4/16/2009      M       2237  44         SOB WEAKNESS
6  4/16/2009      F      21484  41 TOOTH PAINTOOTH PAIN
7  4/16/2009      M      10783  37          RT ARM PAIN
8  4/16/2009      M      12610  65        L FOOT INJURY
9  4/16/2009      F       3495  29 URINARY DIFFICULTIES
10 4/16/2009      F        351  36           PT STS MVA
> b.df[1:10,]
   DATE_OF_DEATH    ID
1      4/19/2009 21676
2      4/19/2009 13717
3      4/19/2009 20498
4      4/19/2009 14281
5      4/19/2009 38848
6      4/20/2009   331
7      4/20/2009  4084
8      4/20/2009 19616
9      4/20/2009 17965
10     4/20/2009 11863
>

a.df will always be larger than b.df.

I want to create a third data frame that is matched on PATIENT_ID from
a.df and ID from b.df.

If there is no match from a.df$PATIENT_ID to b.df$ID, then we omit the
row from the new data.frame.

If there is a match, we include the DATE_OF_DEATH column from b.df.

I've tried all kinds of tricks, but nothing works exactly as I wish.

Thanks in advance,
Sincerely,
Erin


-- 
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodgess at gmail.com