Data commit

Task/Combinations/EchoLisp/combinations.l

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+;;
+;; using the native (combinations) function
+(lib 'list)
+(combinations (iota 5) 3)
+→ ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))
+;;
+;; using an iterator
+;;
+(lib 'sequences)
+(take (combinator (iota 5) 3) #:all)
+→ ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))
+;;
+;; defining a function
+;;
+(define (combine lst p) (cond
+    [(null? lst) null]
+    [(< (length lst) p) null]
+    [(= (length lst) p) (list lst)]
+    [(= p 1) (map list lst)]
+    [else (append
+        (map cons (circular-list (first lst)) (combine (rest lst) (1- p)))
+        (combine (rest lst) p))]))
+
+(combine (iota 5) 3)
+    → ((0 1 2) (0 1 3) (0 1 4) (0 2 3) (0 2 4) (0 3 4) (1 2 3) (1 2 4) (1 3 4) (2 3 4))