Compute per-group cumulative maxs

cummax_g(col, first_indices)

Arguments

col	vector to cumulative max
first_indices	numeric index of first index in each group

per-group cumulative max


v <- c(2, 3, 1, 7, 5)
fi <- c(1, 1, 3, 3, 3)
cummax_g(v, fi)
#> [1] 2 3 1 7 7