Get a bootstrap replicate of the Sample data frame based on the user-specified blockLength.
The bootstrap replicate is made up randomly selected blocks of
data from Sample data frame. Each block includes all the samples in a standard period of time (the blockLength measured in days).
The blocks are created based on the random selection (with
replacement) of starting dates from the full Sample data frame. The bootstrap replicate
has the same number of observations as the original Sample, but some
observations are included once, some are included multiple times, and some are not
included at all.