[R] Simple question on finding duplicates

Peter Ehlers ehlers at ucalgary.ca
Wed Jul 25 23:14:20 CEST 2012

duplicate <- c(0, diff(a[,"col1"]) == 0)

Peter Ehlers

On 2012-07-25 13:05, Jeff wrote:
>     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?
>     Thanks
>     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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