Assumes that at least a total of this many subjects
will be preserved.
condition
A factor vector containing condition labels.
cases_per_second
Assumes that this number of cases are checked out
per second, for estimating the time it takes to run
the exhaustive search; default: 100.
print_info
If TRUE, prints partial calculations as well for
the number of cases and estimated time when removing
1, 2, ... subjects.
max_removed
A named integer vector, containing the maximum number
of subjects that can be removed from each group.
Specify 0 for groups if you want to preserve
all of their subjects. If you do not specify a value
for a group, it defaults to one less than the group size.
Values outside the valid range of 0..(N-1)
(where N is the number of subjects in the group)
are corrected without a warning.
group_sizes
A particular set of group sizes that we know a
matched solution for; min_preserved need not be
specified if this one is.
props
The desired proportions (percentage) of the sample
for each condition; if this and group_sizes are both
specified, the maximum number of cases to considered
by the exhaustive search can be calculated more
precisely.
Value
The maximum number of cases: an integer if not greater than the
maximum integer size (.Machine$integer.max), otherwise a Big Integer
(see the gmp package).
providing 
.