[R] Select rows based on condition

[Rui Barradas]

Hello,

Try

df1 <- read.table(text="
PtName  Visit  Date               Obs          ObsID
S2             1      6/8/2005       KB               3
S2             1      6/8/2005       JB                 5
S3             1     6/8/2005        KB                3
S3             1    6/8/2005         JB                 5      
D1            1     6/12/2007     CD               11
D1            1    6/12/2007       TE                2
D1            1    6/12/2007       MB              4
", header=TRUE)
head(df1)

df2 <- with(df1, sapply(split(df1, list(PtName, Date)),
		                     function(x) if(nrow(x)) x[which(x$ObsID ==
min(x$ObsID)), ]))
df2 <- do.call(rbind, df2)
rownames(df2) <- 1:nrow(df2)
df2

Hope this helps,

Rui Barradas


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