Split data.frame by value
how can I split the following data.frame
df <- data.frame(var1 = c("a", 1, 2, 3, "a", 1, 2, 3, 4, 5, 6, "a", 1, 2), var2 = 1:14)
into lists of / groups of
a 1 1 2 2 3 3 4 a 5 1 6 2 7 3 8 4 9 5 10 6 11 a 12 1 13 2 14
So basically, value "a" in column 1 is the tag / identifier I want to split the data frame on. I know about the split function but that means I have to add another column and since, as can be seen from my example, the size of the groups can vary I do not know how to automatically create such a dummy column to fit my needs.
Any ideas on that?
Cheers,
Sven