data(pistonrings)
attach(pistonrings)
# 40 sample of 5 obs each
qcc.groups(diameter, sample)
# some obs are removed, the result is still a 40x5 matrix but with NAs added
qcc.groups(diameter[-c(1,2,50,52, 199)], sample[-c(1,2,50,52, 199)])
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