Function crosstab 

pub fn crosstab(
    ix: &InfonIndex<RoarPostings>,
    anchor: &str,
    facet_a: &str,
    facet_b: &str,
    k: usize,
) -> Value

Co-occurrence matrix of two facets over an anchor set (top-k values of each by anchor overlap). Like breakdown, the requested facets’ values are shown in full (no high-DF registration filter).