R help - Mar 2009 - which rows are duplicates?

I would like to know which rows are duplicates of each other, not  
simply that a row is duplicate of another row. In the following  
example rows 1 and 3 are duplicates.

 > x <- c(1,3,1)
 > y <- c(2,4,2)
 > z <- c(3,4,3)
 > data <- data.frame(x,y,z)
     x y z
1 1 2 3
2 3 4 4
3 1 2 3

I can't figure out how to get R to tell me that observation 1 and 3  
are the same.  It seems like the "duplicated" and "unique"
functions
should be able to help me out, but I am stumped.

For instance, if I use "duplicated" ...

 > duplicated(data)
[1] FALSE FALSE TRUE

it tells me that row 3 is a duplicate, but not which row it matches.  
How do I figure out WHICH row it matches?

And If I use "unique"...

 > unique(data)
     x y z
1 1 2 3
2 3 4 4

I see that rows 1 and 2 are unique, leaving me to infer that row 3 was  
a duplicate, but again it doesn't tell me which row it was a duplicate  
of (as far as I can tell). Am I missing something?

How can I determine that row 3 is a duplicate OF ROW 1?

Thanks,

Aaron

If you sort the data then the duplicated entries will occur in consecutive
blocks:
> m
  x y z
1 1 2 3
2 3 4 4
3 1 2 3
> m1 <- m[do.call(order, m), ]
> m1
  x y z
1 1 2 3
3 1 2 3
2 3 4 4
> duplicated(m1)
[1] FALSE  TRUE FALSE
>  
When you identify the blocks, the row names will tell you where they occur in
the original data frame.

Bill Venables
http://www.cmis.csiro.au/bill.venables/ 


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Aaron M. Swoboda
Sent: Monday, 30 March 2009 2:07 PM
To: r-help at r-project.org
Subject: [R] which rows are duplicates?

I would like to know which rows are duplicates of each other, not  
simply that a row is duplicate of another row. In the following  
example rows 1 and 3 are duplicates.

 > x <- c(1,3,1)
 > y <- c(2,4,2)
 > z <- c(3,4,3)
 > data <- data.frame(x,y,z)
     x y z
1 1 2 3
2 3 4 4
3 1 2 3

I can't figure out how to get R to tell me that observation 1 and 3  
are the same.  It seems like the "duplicated" and "unique"
functions
should be able to help me out, but I am stumped.

For instance, if I use "duplicated" ...

 > duplicated(data)
[1] FALSE FALSE TRUE

it tells me that row 3 is a duplicate, but not which row it matches.  
How do I figure out WHICH row it matches?

And If I use "unique"...

 > unique(data)
     x y z
1 1 2 3
2 3 4 4

I see that rows 1 and 2 are unique, leaving me to infer that row 3 was  
a duplicate, but again it doesn't tell me which row it was a duplicate  
of (as far as I can tell). Am I missing something?

How can I determine that row 3 is a duplicate OF ROW 1?

Thanks,

Aaron

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At 05:07 30/03/2009, Aaron M. Swoboda wrote:
>I would like to know which rows are duplicates of each other, not
>simply that a row is duplicate of another row. In the following
>example rows 1 and 3 are duplicates.
>
> > x <- c(1,3,1)
> > y <- c(2,4,2)
> > z <- c(3,4,3)
> > data <- data.frame(x,y,z)
>     x y z
>1 1 2 3
>2 3 4 4
>3 1 2 3
Does this do what you want?
 > x <- c(1,3,1)
 > y <- c(2,4,2)
 > z <- c(3,4,3)
 > data <- data.frame(x,y,z)
 > data.u <- unique(data)
 > data.u
   x y z
1 1 2 3
2 3 4 4
 > data.u <- cbind(data.u, set = 1:nrow(data.u))
 > merge(data, data.u)
   x y z set
1 1 2 3   1
2 1 2 3   1
3 3 4 4   2

You need to do a bit more work to get them back into the original row 
order if that is essential.


>I can't figure out how to get R to tell me that observation 1 and 3
>are the same.  It seems like the "duplicated" and
"unique" functions
>should be able to help me out, but I am stumped.
>
>For instance, if I use "duplicated" ...
>
> > duplicated(data)
>[1] FALSE FALSE TRUE
>
>it tells me that row 3 is a duplicate, but not which row it matches.
>How do I figure out WHICH row it matches?
>
>And If I use "unique"...
>
> > unique(data)
>     x y z
>1 1 2 3
>2 3 4 4
>
>I see that rows 1 and 2 are unique, leaving me to infer that row 3 was
>a duplicate, but again it doesn't tell me which row it was a duplicate
>of (as far as I can tell). Am I missing something?
>
>How can I determine that row 3 is a duplicate OF ROW 1?
>
>Thanks,
>
>Aaron
>
>
Michael Dewey
http://www.aghmed.fsnet.co.uk