stop and split generated sequence at repeats - clojure
- by fitzsnaggle
I am trying to make a sequence that will only generate values until it finds the following conditions and return the listed results:
case head =
0 - return {:origin [all generated except 0] :pattern 0}
1 - return {:origin nil :pattern [all-generated-values] }
repeated-value - {:origin [values-before-repeat] :pattern [values-after-repeat]
{
; n = int
; x = int
; hist - all generated values
; Keeps the head below x
(defn trim-head [head x]
(loop [head head]
(if (> head x)
(recur (- head x))
head)))
; Generates the next head
(defn next-head [head x n]
(trim-head (* head n) x))
(defn row [x n]
(iterate #(next-head % x n) n))
; Generates a whole row -
; Rows are a max of x - 1.
(take (- x 1) (row 11 3))
Examples of cases to stop before reaching end of row:
[9 8 4 5 6 7 4] - '4' is repeated so STOP. Return preceding as origin and rest as pattern.
{:origin [9 8] :pattern [4 5 6 7]}
[4 5 6 1] - found a '1' so STOP, so return everything as pattern
{:origin nil :pattern [4 5 6 1]}
[3 0] - found a '0' so STOP
{:origin [3] :pattern [0]}
:else if the sequences reaches a length of x - 1:
{:origin [all values generated] :pattern nil}
The Problem
I have used partition-by with some success to split the groups at the point where a repeated value is found, but would like to do this lazily. Is there some way I can use take-while,
or condp, or the :while clause of the for loop to make a
condition that partitions when it finds repeats?
Some Attempts
(take 2 (partition-by #(= 1 %) (row 11 4)))
(for [p (partition-by #(stop-match? %) head) (iterate #(next-head % x n) n)
:while (or (not= (last p) (or 1 0 n) (nil? (rest p))]
{:origin (first p) :pattern (concat (second p) (last p))}))
# Updates
What I really want to be able to do is find out if a value has repeated and partition the seq without using the index. Is that possible? Something like this -
{
(defn row [x n]
(loop [hist [n]
head (gen-next-head (first hist) x n)
steps 1]
(if (>= (- x 1) steps)
(case head
0 {:origin [hist] :pattern [0]}
1 {:origin nil :pattern (conj hist head)}
; Speculative from here on out
(let [p (partition-by #(apply distinct? %) (conj hist head))]
(if-not (nil? (next p)) ; One partition if no repeats.
{:origin (first p) :pattern (concat (second p) (nth 3 p))}
(recur (conj hist head) (gen-next-head head x n) (inc steps)))))
{:origin hist :pattern nil})))
}
