On R 1.4.1 under Windows 2000 I experience the following:
# this works ok data(iris) merge(iris[1,],iris)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species 1 5.1 3.5 1.4 0.2 setosa
# but try the same thing with this data frame
d.df <- data.frame(x=1:3,y=c("A","D","E"),z=c(6,9,10))
d.df
x y z 1 1 A 6 2 2 D 9 3 3 E 10
# this results in zero rows whereas it should have 1 !!! merge(d.df[1,],d.df)
[1] x y z <0 rows> (or 0-length row.names)
# remove last case and it suddenly works OK merge(d.df[1,],d.df[-3,])
x y z 1 1 A 6
# or remove z and it suddenly works OK merge(d.df[1,-3],d.df[,-3])
x y 1 1 A
# Here is another different problem with merge
# we specified no sorting but the rows are not in the same order as e.df
e.df <- data.frame(x=c(1,4,5,1,3,5),y=c("A","D","E","A","C","E"),z=c(6,9,10,6,8,10))
e.df
x y z 1 1 A 6 2 4 D 9 3 5 E 10 4 1 A 6 5 3 C 8 6 5 E 10
merge(e.df,unique(e.df),sort=F)
x y z 1 1 A 6 2 1 A 6 3 4 D 9 4 5 E 10 5 5 E 10 6 3 C 8
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