Stratified and weighted sampling in dataframes

[bkamins]

@George_Githinji

I ideally want to sample within each group x number of times but if the group size is less than the samples then you would want to pick all the samples in the group and continue without an error.

take_a_sample(df::AbstractDataFrame, size) =
    df[sample(axes(df, 1), min(size, nrow(df)); replace = false, ordered = true), :]