Compare two data sets

<amarkey at uiuc.edu> wrote in
news:20080325101909.BDK93111 at expms2.cites.uiuc.edu:

I would like to compare two data sets saved as text files (example
below) to determine if both sets are identical(or if dat2 is missing
information that is included in dat1) and if they are not identical
list what information is different between the two sets(ie output
"a1", "a3" as the differing information).  The overall purpose would
be to remove "a1" and "a3" from dat 1 so both dat1 and dat2 are the
same.  My R abilities are somewhat limited so any suggestions are
greatly appreciated. 

I do not understand what it would mean to remove elements so "they 
would look the same". Why wouldn't you just use the smaller set?

Alysta

dat1
a1
a2
a3
a4
a5
a6

dat2
a2
a4
a5
a6

You might want to look at the %in% function. These examples created 
with neither dat1 nor dat2 being proper subsets of the other.

dat1 <- paste('a', 1:6, sep='')
dat2 <- paste('a', c(2,4:6,8,9,10), sep='')

dat1

[1] "a1" "a2" "a3" "a4" "a5" "a6"

dat2

[1] "a2"  "a4"  "a5"  "a6"  "a8"  "a9"  "a10"


dat2 %in% dat1
#[1]  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE

dat1 %in% dat2
#[1] FALSE  TRUE FALSE  TRUE  TRUE  TRUE

### And then use the logical vectors as index arguments
### to  first get the common elements

dat1[dat1 %in% dat2]

[1] "a2" "a4" "a5" "a6"

dat2[dat2 %in% dat1]

[1] "a2" "a4" "a5" "a6"

### And then to find the non-shared elements

dat2[!(dat2 %in% dat1)]

[1] "a8"  "a9"  "a10"

dat1[!(dat1 %in% dat2)]

[1] "a1" "a3"

David Winsemius