[R] UNIX diff function

[Dennis Fisher]

Colleagues,

(R: 2.13.0; OS X)

I often receive sequential datasets in which there are new rows interposed between existing rows.  For example:
	SET1 <- data.frame(list(LETTERS=LETTERS[c(1:4, 6:10)], NUMBERS=c(1:4, 6:10)))
	SET2 <- data.frame(list(LETTERS=LETTERS[1:10], NUMBERS=1:10))

> SET1
  LETTERS NUMBERS
1       A       1
2       B       2
3       C       3
4       D       4
5       F       6
6       G       7
7       H       8
8       I       9
9       J      10

> SET2
   LETTERS NUMBERS
1        A       1
2        B       2
3        C       3
4        D       4
5        E       5
6        F       6
7        G       7
8        H       8
9        I       9
10       J      10

As you can see, the row containing E and 5 was inserted into the second set.  The UNIX diff command identifies the differences quite readily.  Obviously, the R diff function does not do this.  However, one kluge that I use is to paste together all the entries in each row, then perform a setdiff on the two resulting vectors.  Assuming that no rows are duplicated (which would true in my data), my approach works but is it cumbersome.  

I suspect that someone on this board has thought of a more clever approach to this (or perhaps some function already exists).  Any help would be appreciated.

Thanks.

Dennis


Dennis Fisher MD
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