JaccardSimilarity.kt

fun jaccardSimilarity(first: Array<Int>, second: Array<Int>): Float {
    val s1 = first.toSet()
    val s2 = second.toSet()
    return s1.intersect(s2).size / s1.union(s2).size.toFloat()
}

class Encoder {
    var base = 0

    fun encode(categories: Set<String>) =
        categories.mapIndexed { index: Int, category: String -> base + index }.toSortedSet().apply {
            base += size
        }
}

data class Item(val category: String, val shopName: String)

val A = Item("car", "ShopA")
val B = Item("toy", "ShopB")
val C = Item("toy", "ShopC")

val allItems = listOf(A, B, C)

val encoder = Encoder()

val categories = allItems.map { it.category }.toSortedSet()
val allShops = allItems.map { it.shopName }.toSortedSet()

val encodedCategories = encoder.encode(categories)
val encodedShops = encoder.encode(allShops)

val categoriesMap = categories.mapIndexed { index: Int, category: String -> category to encodedCategories.elementAt(index) }.toMap()
val shopsMap = allShops.mapIndexed { index: Int, shop: String -> shop to encodedShops.elementAt(index) }.toMap()

fun Item.encode(): Array<Int> = arrayOf(categoriesMap[category]!!, shopsMap[shopName]!!)

println("A -> B ${jaccardSimilarity(A.encode(), B.encode())}  ")
println("A -> C ${jaccardSimilarity(A.encode(), C.encode())}  ")
println("B -> C ${jaccardSimilarity(B.encode(), C.encode())}  ")
println("C -> B ${jaccardSimilarity(C.encode(), B.encode())}  ")