Function datafusion_physical_expr_common::aggregate::groups_accumulator::accumulate::accumulate_indices

pub fn accumulate_indices<F>(
    group_indices: &[usize],
    nulls: Option<&NullBuffer>,
    opt_filter: Option<&BooleanArray>,
    index_fn: F,
)
where
    F: FnMut(usize) + Send,

This function is called to update the accumulator state per row when the value is not needed (e.g. COUNT)

F: Invoked like `value_fn(group_index) for all non null values passing the filter. Note that no tracking is done for null inputs or which groups have seen any values

See NullState::accumulate, for more details on other arguments.