That's basically the same as the first solution, in terms of how it works
under the hood.
If the desire is for the output to share structure with the input, not just
the maps but the vector as well, then you need to do something a bit more
complicated. First you need to find the map you want, and return its index
in the vector (assuming it will be unique if present). Then you need to use
assoc-in with the index, like (assoc-in v [idx :c] 50) or whatever.
If there may be more than one map that should be adjusted, you could return
a seq of indices and repeatedly assoc-in, but I doubt this would give
superior efficiency unless the vector was typically huge and the number of
maps needing changes typically much smaller. With million-element vectors
and two or three maps needing updating it would likely be preferable to the
(vec (for ...)) approach. With dozen-element vectors with half a dozen maps
needing updating I'd go with (vec (for ...)).
On Tue, Jul 30, 2013 at 4:58 PM, Jim - FooBar(); <jimpil1...@gmail.com>wrote:
> Hi,
>
> how about ....
>
> (vec
> (for [{:keys [a b c] :as m} aa]
> (if (= a 50) (assoc m :c 3) m)))
>
> :)
> Jim
>
>
>
> On 30/07/13 18:53, cej38 wrote:
>
> Suppose I have a vector of maps (this could also be a vector of records)
>
> (def aa [{:a 0 :b 0 :c 0} {:a 50 :b 0 :c 0} {:a 100 :b 0 :c 0}])
>
> and I want to go in an change the value of associated with :c when :a
> has a value of 50, so that the final col of maps looks like
>
> [{:a 0 :b 0 :c 0} {:a 50 :b 0 :c 3} {:a 100 :b 0 :c 0}].
>
>
>
> I came up with a function that does this:
>
> (defn find-assoc-in
> [k v mv]
> (let [f #(if (= ((first k) %) (first v))
> (assoc % (second k) (second v))
> %)]
> (map f mv)))
>
>
> (find-assoc-in [:a :c] [50 3] aa)
>
>
> The problem with this function is that it potentially does a lot
> of unnecessary copying of elements that aren't changed, and thus has a lot
> of garbage collection. I would like help coming up with something that
> does much less garbage collection.
>
>
> Will someone please point out a better way of doing this?
>
> --
> --
> 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/groups/opt_out.
>
>
>
>
> --
> --
> 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/groups/opt_out.
>
>
>
--
--
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/groups/opt_out.
