Set-level composition dynamics: how much of the group's membership mass entered or exited between the two snapshots.
Arguments
- data
Member-level long data covering both snapshots.
- group, member, time
Column names (strings): group id, member id, and the time variable.
- weight
Column name (string) of the raw weight, or
NULLfor equal weights.- t1, t2
The two time values to compare.
- x
Not used (turnover is a property of the roster and weights alone).
Value
A data frame with one row per group: entry_mass (weight mass
of entrants at t2), exit_mass (weight mass of exiters at
t1), jaccard_dist (1 - |intersection| / |union| of the
member sets), and realloc_l1 (\(\frac{1}{2}\sum_k |\Delta w_k|\),
the total variation distance between the two weight measures).