How to select rows by group with the minimum value and containing NAs in R

Question

Here is an example:

set.seed(123)    
data<-data.frame(X=rep(letters[1:3], each=4),Y=sample(1:12,12),Z=sample(1:100, 12))
data[data==3]<-NA
         


        

Answer 1

This does not select the rows using an index but returns the values you want...

ddply(data, .(X), summarise, min=min(Y, na.rm=T))

  X min
1 a   5
2 b   1
3 c   4

EDIT AFTER COMMENT: To select the whole rows you may:

ddply(data, .(X), function(x) arrange(x, Y)[1, ])

  X Y  Z
1 a 4 68
2 b 1  4
3 c 2 64

Or

data$index <- 1L:nrow(data)
i <- by(data, data$X, function(x) x$index[which.min(x$Y)] )
data[i, ]

   X Y  Z index
1  a 4 68     1
6  b 1  4     6
10 c 2 64    10