Re: filter but for non-sequences
On Monday, October 27, 2014 3:00:40 AM UTC-4, Marcus Magnusson wrote: I don't see how the macro version would offer any performance benefits - in both cases, x is evaluated once and pred is called once. Am I missing something? Nah. Someone upthread suggested a macro, for some reason. I don't see much advantage either, other than saving the overhead of a function call and having exactly the same performance as just writing (if (pred x) x). -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: filter but for non-sequences
Hi Sam, I’m not sure I understand. If not for sequences, then what for? `(if (pred x) x)` looks like it’s missing an else-clause; so I don’t know what happens when (not (pred x)). From the rest of your e-mail it sounds a little bit like you might want (get m x x)? (i.e. get me x if x isn’t in m; otherwise give me the value mapped to x in m). hth lvh On 24 Oct 2014, at 06:06, Sam Raker sam.ra...@gmail.com wrote: Is there anything simpler/more idiomatic than `(if (pred x) x)`? What I really want is something better than `(if (= (get a-map a-key) a-val) a-map)`/`(if (= (get-in a-map some-keys) a-val) a-map)`, but that might be too specific to have been 'cached' somewhere. -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. signature.asc Description: Message signed with OpenPGP using GPGMail
Re: filter but for non-sequences
I think the point is to get nil if x does not satisfy some predicate. The best option would depend on the context in which these expressions are used, but one option would be to write your predicates to return the input as the truthy value (and nil otherwise). On Friday, 24 October 2014, Laurens Van Houtven _...@lvh.io wrote: Hi Sam, I’m not sure I understand. If not for sequences, then what for? `(if (pred x) x)` looks like it’s missing an else-clause; so I don’t know what happens when (not (pred x)). From the rest of your e-mail it sounds a little bit like you might want (get m x x)? (i.e. get me x if x isn’t in m; otherwise give me the value mapped to x in m). hth lvh On 24 Oct 2014, at 06:06, Sam Raker sam.ra...@gmail.com javascript:; wrote: Is there anything simpler/more idiomatic than `(if (pred x) x)`? What I really want is something better than `(if (= (get a-map a-key) a-val) a-map)`/`(if (= (get-in a-map some-keys) a-val) a-map)`, but that might be too specific to have been 'cached' somewhere. -- 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 javascript:; 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 javascript:; 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 unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com javascript:;. For more options, visit https://groups.google.com/d/optout. -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: filter but for non-sequences
I think the point is to get nil if x does not satisfy some predicate. --
exactly.
I basically want something like `if-let`, but which returns x instead of
f(x). `(if-let [m-with-k (contains? m k)]...` results in `m-with-k`
evaluating to `true`, not `m`. I *think* it's better to reject something
that doesn't meet your criteria early, as opposed to guarding against not
accidentally doing something like `(.toUpper {:foo m})` and getting an
error every step of the way.
But like I said, I'm totally willing to believe there's a more
idiomatic/appropriate way of doing things.
On Friday, October 24, 2014 4:59:33 AM UTC-4, Gary Verhaegen wrote:
I think the point is to get nil if x does not satisfy some predicate.
The best option would depend on the context in which these expressions are
used, but one option would be to write your predicates to return the input
as the truthy value (and nil otherwise).
On Friday, 24 October 2014, Laurens Van Houtven _...@lvh.io wrote:
Hi Sam,
I’m not sure I understand. If not for sequences, then what for? `(if
(pred x) x)` looks like it’s missing an else-clause; so I don’t know what
happens when (not (pred x)).
From the rest of your e-mail it sounds a little bit like you might want
(get m x x)? (i.e. get me x if x isn’t in m; otherwise give me the value
mapped to x in m).
hth
lvh
On 24 Oct 2014, at 06:06, Sam Raker sam.ra...@gmail.com wrote:
Is there anything simpler/more idiomatic than `(if (pred x) x)`? What I
really want is something better than `(if (= (get a-map a-key) a-val)
a-map)`/`(if (= (get-in a-map some-keys) a-val) a-map)`, but that might be
too specific to have been 'cached' somewhere.
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Re: filter but for non-sequences
On 24 Oct 2014, at 15:05, Sam Raker sam.ra...@gmail.com wrote: I think the point is to get nil if x does not satisfy some predicate. -- exactly. … and shorter than (when (p x) x)? If you can come up for a good name for that, I guess you could macro it? :-) hth lvh signature.asc Description: Message signed with OpenPGP using GPGMail
Re: filter but for non-sequences
(defn if-its [pred x] (if (pred x) x)) = (if-its even? 4) 4 = (if-its even? 5) nil Or, if you want a macro for performance reasons or something, and don't mind the loss of e.g. (filter identity (map (partial if-its pred) coll)): (defmacro if-its [pred x] `(let [a# ~x] (if (~pred a#) a#))) -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
filter but for non-sequences
Is there anything simpler/more idiomatic than `(if (pred x) x)`? What I really want is something better than `(if (= (get a-map a-key) a-val) a-map)`/`(if (= (get-in a-map some-keys) a-val) a-map)`, but that might be too specific to have been 'cached' somewhere. -- 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 --- You received this message because you are subscribed to the Google Groups Clojure group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
