R help - May 2010 - How to extract rows from data frame based on unique variable groupings

R community,
 
I would like to know how to extract rows from a data frame (DF) such that 
each row in the new data frame (D.F) represents the first instance of 
a unique variable pairing in the original dataframe (ordered first by 
variable V1 then by variable V2). The unique function does not seem 
to be able to accomplish this. I imagine there must be a simple solution for
this,
but I can't seem to find it. 
 
Thank you,
 
Mike
 
 
DF <-
structure(list(V1 = c(1, 1, 1, 1, 2, 2, 2, 2), V2 = c(1, 1, 2, 2, 1, 1, 2, 2), 
V3 = c(1L, 8L, 4L, 3L, 6L, 2L, 7L, 5L), V4 = c(8L, 3L, 6L, 1L, 2L, 4L, 5L, 7L)),
.Names = c("V1", "V2", "V3", "V4"),
row.names = c(NA, -8L), class = "data.frame")
 

D.F <-
structure(list(V.1 = c(1, 1, 2, 2), V.2 = c(1, 2, 1, 2), V.3 = c(1, 4, 6, 7), 
V.4 = c(8, 6, 2, 5)), .Names = c("V.1", "V.2",
"V.3", "V.4"), row.names = c(NA, -4L),
class = "data.frame") 		 	   		  
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Tena koe Mike

duplicated() might be what you require.

HTH ...

Peter Alspach
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Michael H
> Sent: Friday, 21 May 2010 6:37 a.m.
> To: r-help at r-project.org
> Subject: [R] How to extract rows from data frame based on unique
> variable groupings
> 
> 
> 
> R community,
> 
> I would like to know how to extract rows from a data frame (DF) such
> that
> each row in the new data frame (D.F) represents the first instance of
> a unique variable pairing in the original dataframe (ordered first by
> variable V1 then by variable V2). The unique function does not seem
> to be able to accomplish this. I imagine there must be a simple
> solution for this,
> but I can't seem to find it.
> 
> Thank you,
> 
> Mike
> 
> 
> DF <-
> structure(list(V1 = c(1, 1, 1, 1, 2, 2, 2, 2), V2 = c(1, 1, 2, 2, 1,
1,
> 2, 2),
> V3 = c(1L, 8L, 4L, 3L, 6L, 2L, 7L, 5L), V4 = c(8L, 3L, 6L, 1L, 2L, 4L,
> 5L, 7L)),
> .Names = c("V1", "V2", "V3", "V4"),
row.names = c(NA, -8L), class > "data.frame")
> 
> 
> D.F <-
> structure(list(V.1 = c(1, 1, 2, 2), V.2 = c(1, 2, 1, 2), V.3 = c(1, 4,
> 6, 7),
> V.4 = c(8, 6, 2, 5)), .Names = c("V.1", "V.2",
"V.3", "V.4"),
row.names
> = c(NA, -4L),
> class = "data.frame")
> _________________________________________________________________
> Hotmail is redefining busy with tools for the New Busy. Get more from
> your inbox.
> 
> N:WL:en-US:WM_HMP:042010_2
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> PLEASE do read the posting guide http://www.R-project.org/posting-
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> and provide commented, minimal, self-contained, reproducible code.

I hope this is what you want.

## Exclude replicated rows
(DF1 <- unique(DF))

## Sort the data
(DF2 <- DF1[order(DF1$V1, DF1$V2, DF1$V3, DF1$V4),])

-----
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