| gl {base} | R Documentation | 
Generate factors by specifying the pattern of their levels.
gl(n, k, length = n*k, labels=1:n, ordered=FALSE)
n | 
an integer giving the number of levels. | 
k | 
an integer giving the number of replications. | 
length | 
an integer giving the length of the result. | 
labels | 
an optional vector of labels for the resulting factor levels. | 
ordered | 
a logical indicating whether the result should be ordered or not. | 
The result has levels from 1 to n with each value
replicated in groups of length k out to a total length of
length.
gl is modelled on the GLIM function of the same name.
the underlying factor(.).
# First control, then treatment:
gl(2,8, label=c("Ctnrl","Treat"))
# 20 alternating 1s and 2s
gl(2, 1, 20)
# alternating pairs of 1s and 2s
gl(2, 2, 20)