Cartesian product of two or more lists: Difference between revisions

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 =={{header|Groovy}}==
-'''Solution:'''
+'''Solution:'''<br>
+The following ''CartesianCategory'' class allows for modification of regular ''Iterable'' interface behavior, overloading ''Iterable'''s ''multiply'' (*) operator to perform a Cartesian Product when the second operand is also an ''Iterable''.
-<lang groovy>def cartProd(Iterable ... lists) {
+<lang groovy>class CartesianCategory {
-    assert lists
+    static Iterable multiply(Iterable a, Iterable b) {
-    def order = lists.size()
-    assert order > 1
+        assert [a,b].every { it != null }
-    def dims = lists*.size()
+        def (m,n) = [a.size(),b.size()]
+        (0..<(m*n)).inject([]) { prod, i -> prod << [a[i.intdiv(n)], b[i%n]].flatten() }
-    if (order == 2) {
-        def (n0,n1) = dims
-        (0..<(n0*n1)).inject([]) { prod, i -> prod << [lists[0][i.intdiv(n1)],lists[1][i%n1]] }
-    } else {
-        def (l1,l2) = lists[0..1]
-        Iterable[] newLists = [cartProd(l1,l2)] + lists[2..<order]
-        cartProd(newLists).collect { it.flatten() }
     }
 }</lang>
-'''Test:'''
+'''Test:'''<br>
+The ''mixin'' method call is necessary to make the multiply (*) operator work.
-<lang groovy>println "[1, 2] × [3, 4] = ${cartProd([1, 2], [3, 4])}"
+<lang groovy>Iterable.metaClass.mixin CartesianCategory
-println "[3, 4] × [1, 2] = ${cartProd([3, 4], [1, 2])}"
-println "[1, 2] × [] = ${cartProd([1, 2], [])}"
-println "[] × [1, 2] = ${cartProd([], [1, 2])}"
+println "[1, 2] × [3, 4] = ${[1, 2] * [3, 4]}"
-println "[1776, 1789] × [7, 12] × [4, 14, 23] × [0, 1] = ${cartProd([1776, 1789], [7, 12], [4, 14, 23], [0, 1])}"
+println "[3, 4] × [1, 2] = ${[3, 4] * [1, 2]}"
-println "[1, 2, 3] × [30] × [500, 100] = ${cartProd([1, 2, 3], [30], [500, 100])}"
+println "[1, 2] × [] = ${[1, 2] * []}"
-println "[1, 2, 3] × [] × [500, 100] = ${cartProd([1, 2, 3], [], [500, 100])}"
+println "[] × [1, 2] = ${[] * [1, 2]}"
+println "[1776, 1789] × [7, 12] × [4, 14, 23] × [0, 1] = ${[1776, 1789] * [7, 12] * [4, 14, 23] * [0, 1]}"
+println "[1, 2, 3] × [30] × [500, 100] = ${[1, 2, 3] * [30] * [500, 100]}"
+println "[1, 2, 3] × [] × [500, 100] = ${[1, 2, 3] * [] * [500, 100]}"
 println "[John,Paul,George,Ringo] × [Emerson,Lake,Palmer] × [Simon,Garfunkle] = ["
-cartProd(["John","Paul","George","Ringo"], ["Emerson","Lake","Palmer"], ["Simon","Garfunkle"]).each { println "\t${it}," }
+( ["John","Paul","George","Ringo"] * ["Emerson","Lake","Palmer"] * ["Simon","Garfunkle"] ).each { println "\t${it}," }
 println "]"</lang>
 '''Output:'''