Theta sketch set operations

Combine two theta() sketches into a new compact theta_sketch result, without mutating either input. a and b must be Theta sketches created with the same seed (a mismatch raises datasketches_seed_mismatch).

Usage

theta_union(a, b, lg_k = NULL)

theta_intersection(a, b)

theta_difference(a, b)

theta_jaccard(a, b)

Arguments

a, b

theta_sketch objects created with the same seed.

lg_k

For theta_union(), log2 of the nominal number of entries for the union's internal sketch, a single whole number in [5, 26]. Defaults to the larger of a and b's configured lg_k (or 12 for compact inputs).

Value

A compact theta_sketch object (theta_union(), theta_intersection(), theta_difference()), or a named numeric vector c(lower_bound, estimate, upper_bound) (theta_jaccard()).

Details

• theta_union(a, b) estimates the size of the union union(A, B).

• theta_intersection(a, b) estimates the size of the intersection intersection(A, B).

• theta_difference(a, b) estimates the size of the set difference A \\ B (elements in A but not B).

• theta_jaccard(a, b) estimates the Jaccard similarity index J(A, B) = |intersection(A, B)| / |union(A, B)|, returning a named numeric vector c(lower_bound, estimate, upper_bound) for a ~95% confidence interval.

Examples

a <- theta(1:1000)
b <- theta(501:1500)
theta_union(a, b)$estimate()
#> [1] 1500
theta_intersection(a, b)$estimate()
#> [1] 500
theta_difference(a, b)$estimate()
#> [1] 500
theta_jaccard(a, b)
#> lower_bound    estimate upper_bound 
#>   0.3333333   0.3333333   0.3333333