Re: Partitioning a list when the result of a predicate becomes a certain value.
Thanks for the replies guys - has given me things to mull over. On Thursday, 10 May 2012 22:11:18 UTC+1, Ant wrote: Hi all, I am battering my head against the following problem which I'm sure is straightforward if only I knew how. I want to partition the following list: '(aa123 x y z bb123 ccq23 3 yg) into the following: ((aa123 x y z) (bb123) (ccq23 3 yg)) The predicate is: #(re-matches #^(\w)\1.* %) partition-by doesn't work, since it splits the sequence when the result of applying the predicate changes. I want to partition when the predicate becomes a particular value. Any clues on how to accomplish this would be gratefully received! Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
I think you'd just have to do it manually with a reduce Something like this should work. (defn foldfn [i n] (let [result (first i) current (second i)] (if (re-matches #^(\w)\1.* n) (if (= [] current) [result [n]] [(conj result current) [n]]) [result (conj current n)]))) (defn partition-lst [lst] (let [reduced (reduce foldfn [[][]] lst) result (first reduced) current (second reduced)] (if (= current []) result (conj result current -- Stephen Olsen Sent with Sparrow (http://www.sparrowmailapp.com/?sig) On Thursday, May 10, 2012 at 4:11 PM, Ant wrote: Hi all, I am battering my head against the following problem which I'm sure is straightforward if only I knew how. I want to partition the following list: '(aa123 x y z bb123 ccq23 3 yg) into the following: ((aa123 x y z) (bb123) (ccq23 3 yg)) The predicate is: #(re-matches #^(\w)\1.* %) partition-by doesn't work, since it splits the sequence when the result of applying the predicate changes. I want to partition when the predicate becomes a particular value. Any clues on how to accomplish this would be gratefully received! Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com (mailto:clojure@googlegroups.com) Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com (mailto:clojure+unsubscr...@googlegroups.com) For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Partitioning a list when the result of a predicate becomes a certain value.
Hi all, I am battering my head against the following problem which I'm sure is straightforward if only I knew how. I want to partition the following list: '(aa123 x y z bb123 ccq23 3 yg) into the following: ((aa123 x y z) (bb123) (ccq23 3 yg)) The predicate is: #(re-matches #^(\w)\1.* %) partition-by doesn't work, since it splits the sequence when the result of applying the predicate changes. I want to partition when the predicate becomes a particular value. Any clues on how to accomplish this would be gratefully received! Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
After posting, I had the idea of checking out the source for partition- by, and solved the problem: (defn partition-when Applies f to each value in coll, splitting it each time f returns the specified value. Returns a lazy seq of partitions. [f value coll] (lazy-seq (when-let [s (seq coll)] (let [run (cons (first s) (take-while #(not= value (f %)) (next s)))] (cons run (partition-when f value (seq (drop (count run) s ) ) ) ) So, I can see basically how this function works, but am not sure what the when-let gives you. Could someone explain? The documentation makes no sense to me at the moment: (when-let bindings body) bindings = binding-form test When test is true, evaluates body with binding-form bound to the value of test What test? Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
(when-let [s (seq coll)] (let [run (cons (first s) (take-while #(not= value (f %)) (next s)))] (cons run (partition-when f value (seq (drop (count run) s ) ) ) ) ... What test? (seq coll) is the test here. when-let (and if-let, etc) bind only when the right hand side is truthy. (when-let [x true] (println this prints)) (when-let [x false] (println this does not print)) It's a common shortcut for: (let [x (something-something)] (when x )) jack. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
(seq coll) is the test, if the collection is empty seq returns nil, hence nothing gets done in the (let ...) form. Luc After posting, I had the idea of checking out the source for partition- by, and solved the problem: (defn partition-when Applies f to each value in coll, splitting it each time f returns the specified value. Returns a lazy seq of partitions. [f value coll] (lazy-seq (when-let [s (seq coll)] (let [run (cons (first s) (take-while #(not= value (f %)) (next s)))] (cons run (partition-when f value (seq (drop (count run) s ) ) ) ) So, I can see basically how this function works, but am not sure what the when-let gives you. Could someone explain? The documentation makes no sense to me at the moment: (when-let bindings body) bindings = binding-form test When test is true, evaluates body with binding-form bound to the value of test What test? Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -- Softaddictslprefonta...@softaddicts.ca sent by ibisMail from my ipad! -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
https://github.com/flatland/useful/blob/develop/src/useful/seq.clj#L189 is a more general version of partition-by, which can easily handle your requirements. On May 10, 2:11 pm, Ant ant...@gmail.com wrote: Hi all, I am battering my head against the following problem which I'm sure is straightforward if only I knew how. I want to partition the following list: '(aa123 x y z bb123 ccq23 3 yg) into the following: ((aa123 x y z) (bb123) (ccq23 3 yg)) The predicate is: #(re-matches #^(\w)\1.* %) partition-by doesn't work, since it splits the sequence when the result of applying the predicate changes. I want to partition when the predicate becomes a particular value. Any clues on how to accomplish this would be gratefully received! Thanks, Anthony. -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: Partitioning a list when the result of a predicate becomes a certain value.
On May 10, 3:19 pm, Jack Moffitt j...@metajack.im wrote: (when-let [s (seq coll)] (let [run (cons (first s) (take-while #(not= value (f %)) (next s)))] (cons run (partition-when f value (seq (drop (count run) s ) ) ) ) ... What test? (seq coll) is the test here. when-let (and if-let, etc) bind only when the right hand side is truthy. (when-let [x true] (println this prints)) (when-let [x false] (println this does not print)) It's a common shortcut for: (let [x (something-something)] (when x )) Not quite true in the general case, though. Consider (let [x 1] (if-let [x foo] x ;; should be foo x)) ;; should be 1 -- You received this message because you are subscribed to the Google Groups Clojure group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
