[R] Simple question on finding duplicates

arun smartpink111 at yahoo.com
Wed Jul 25 22:26:48 CEST 2012

Try this:

  a <- data.frame( col1 = c(1,2,3,3,4))
a<-within(a, duplicate<-c(0,ifelse(diff(a$col1)==0,1,0)))
  col1 duplicate
1    1         0
2    2         0
3    3         0
4    3         1
5    4         0

----- Original Message -----
From: Jeff <r at jp.pair.com>
To: r-help at r-project.org
Sent: Wednesday, July 25, 2012 4:05 PM
Subject: [R] Simple question on finding duplicates

   I'm  trying  to find duplicate values in a column of a data frame. For
   example, dataframe (a) below has two 3's. I would like to mark each value of
   each row as either not being a duplicate of the one before (0), or as a
   duplicate (1) - for example, as in dataframe (b). In SPSS, I would simply
   compare each value to it's "lagged" value, but I can't figure out how to do
   this with R.
   Can someone point me in the right direction?
   a <- data.frame( col1 = c(1,2,3,3,4))
   b <- data.frame( col1 = c(1,2,3,3,4), duplicate = c(0,0,0,1,0))
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