Sample a random proportion of the data, keeping at least one observation
GroupedSampleFracAtLeastOneSample(d_subset, prop, is.random = TRUE)A dtta.frame from which a small sample is to be returned
A number between 0 and 1, being the desired sampling fraction.
a boolean. If TRUE, a random sample is drawn, else it takes the head() of the data
A random sample from the data, of proportion prop, but always returning at least one observation even if prop is too low.
This function is designed to allow its use with group splitting or do.by methods.