Re: possibly non-intuitive behaviour of clojure.set/rename-keys and possible enhancement suggestion
Using the array-map sounds like a good work-around when you know there are
potential key collisions. It would also allow you to swap keys reliably using
a temporary key.
(rename-keys {:a 1 :b 2 :c 3} (array-map :a :tmp :b :a :tmp :b))
;; {:b 1, :a 2, :c 3}
The larger question is: Should rename-keys handle the collisions for you? I
think it was probably a pragmatic decision not to handle collisions in order to
have better performance for the (usual) collision-free case with a small number
of changes. It would be good if the doc for rename-keys warned that behavior
with key collisions is not defined.
On May 10, 2011, at 10:56 PM, Sunil S Nandihalli wrote:
> (defn rename-keys [mp kmap-fn]
> (into {} (map (fn [[key val]] [(kmap-fn key) val]) mp)))
By the way, the suggested implementation doesn't work for keys that don't
change (that is, when some keys that are left out of the kmap). You get a nil
for the key in that case. I think it would work if the old key was used when
you got a nil for the new key. However, you still have an issue if someone
actually wants to use nil or false as a new key. (Not likely, but you'd need to
document it.)
(defn truthy-rename-keys [mp kmap-fn]
(into {} (map (fn [[key val]] [(or (kmap-fn key) key) val]) mp)))
I did a few timings and it looks like performance is similar for rename-keys
and truthy-rename-keys when kmap has lots of key changes, but rename-keys is
much faster when there are only a couple of key changes. That makes sense as
rename-keys is reducing over the kmap, but truthy-rename-keys is mapping over
the original map.
My conclusion is that it's probably not worth "fixing" rename-keys. A little
extra documentation would be helpful. I updated the ClojureDocs.org entry with
a couple of new examples with key collisions.
Regards,
Steve Miner
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Re: possibly non-intuitive behaviour of clojure.set/rename-keys and possible enhancement suggestion
This renames keys to avoid collisions, using an array map to preserve
the order of the keys:
user=> (rename-keys {1 :a 2 :b 3 :c} (array-map 3 4 2 3 1 2))
{2 :a, 3 :b, 4 :c}
On May 11, 7:22 am, Armando Blancas wrote:
> > (clojure.set/rename-keys {1 :a 2 :b 3 :c} {1 2 2 3 3 4})
>
> > returns
>
> > {4 :a}
>
> That's caused by the collision between new and existing keys. Renaming
> 1 to 2 blows [2 :b]: {2 :a, 3 :c}; then renaming 2 to 3 blows [3 :c],
> leaving {3 :a}; and the last just renames 3 to 4: {4 :a}.
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Re: possibly non-intuitive behaviour of clojure.set/rename-keys and possible enhancement suggestion
> (clojure.set/rename-keys {1 :a 2 :b 3 :c} {1 2 2 3 3 4})
>
> returns
>
> {4 :a}
That's caused by the collision between new and existing keys. Renaming
1 to 2 blows [2 :b]: {2 :a, 3 :c}; then renaming 2 to 3 blows [3 :c],
leaving {3 :a}; and the last just renames 3 to 4: {4 :a}.
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Re: possibly non-intuitive behaviour of clojure.set/rename-keys and possible enhancement suggestion
I agree there are going to be problems with implementation as-well .. for
example if not all the keys in the current map are not in the kmap ... but
situation can be handled however, if we passed a function this is going to
be harder .. ..
On Wed, May 11, 2011 at 8:26 AM, Sunil S Nandihalli <
sunil.nandiha...@gmail.com> wrote:
> Hello everybody,
> I tried to use clojure.set/rename-keys .. I kind of felt it has a little
> odd behaviour... for example ..
>
> (clojure.set/rename-keys {1 :a 2 :b 3 :c} {1 2 2 3 3 4})
>
> returns
>
> {4 :a}
>
> I think a more reasonable behavior would be to have it return
>
> {2 :a 3 :b 4 :c}
>
> a further enhancement suggestion would be to accept a function instead of a
> map that way even the existing code will not break since the map already
> implements IFn
>
> a sample implementation which takes the above into account would be ..
>
> (defn rename-keys [mp kmap-fn]
> (into {} (map (fn [[key val]] [(kmap-fn key) val]) mp)))
>
>
> Thanks,
> Sunil.
>
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possibly non-intuitive behaviour of clojure.set/rename-keys and possible enhancement suggestion
Hello everybody,
I tried to use clojure.set/rename-keys .. I kind of felt it has a little
odd behaviour... for example ..
(clojure.set/rename-keys {1 :a 2 :b 3 :c} {1 2 2 3 3 4})
returns
{4 :a}
I think a more reasonable behavior would be to have it return
{2 :a 3 :b 4 :c}
a further enhancement suggestion would be to accept a function instead of a
map that way even the existing code will not break since the map already
implements IFn
a sample implementation which takes the above into account would be ..
(defn rename-keys [mp kmap-fn]
(into {} (map (fn [[key val]] [(kmap-fn key) val]) mp)))
Thanks,
Sunil.
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