Creating a hash-map with conditional keys
Hello,
I am trying to figure out how to make the following elegantly in clojure.
I have a hash-map which has some key-value pairs and I would like to append
to that hash-map a couple more key-value pairs IF some specific condition
is met. For example, the create-map creates the main hash-map but i would
like *to merge* the map with the value returned from create-key-value, if
the condition inside that function is met.
(defn create-key-value [value]
(when (some-condition-true) {:extra-key "extra-value"))
> (defn create-map []
{:foo "a"
:bar "b"})
The final, merged, map should look like this *if* create-key-value returned
the :extra-key
{:foo "a", :bar "b", :extra-key "extra-value"}
...or if it didn't to return this:
> {:foo "a", :bar "b"}
I did find a proposed solution on a stackoverflow
post,
but I am not sure if that's the most elegant way.
Thank you for your time.
Regards,
Ryan
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Re: Creating a hash-map with conditional keys
Hi, merge works with nil. So (merge (create-map) (create-key-value "some-value")) should work as you intend with the functions as they are defined now. Kind regards Meikel -- -- 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.
Re: Creating a hash-map with conditional keys
Thanks Meikel for your reply.
It wasn't clear on my example, but I wish to use *merge *inside my
create-map function. Do you think I should bind my hash-map to a let
variable first and then apply merge, or do you have another proposal? What
i mean is this:
(defn create-key-value [value]
(when (some-condition-true) {:extra-key value))
(defn create-map []
> (let [my-map {:foo "a" :bar "b"}]
> (merge my-map (create-key-value "some-value")))
Is the above "clojurish" or is there a better way? For example if the
my-map was a big hash-map, and not with just two pairs, wouldn't it be ugly
with the above way? or..it's just fine and no better way is possible?
Ryan
On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
(kotarak) wrote:
>
> Hi,
>
> merge works with nil. So (merge (create-map) (create-key-value
> "some-value")) should work as you intend with the functions as they are
> defined now.
>
> Kind regards
> Meikel
>
>
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Re: Creating a hash-map with conditional keys
I'd often just write it like this:
(defn create-map []
> (merge {:foo "a"
>:bar "b"
>... many more keys}
> (when (some-condition-true)
> {:extra-key value)))
Alex
On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
> Thanks Meikel for your reply.
>
> It wasn't clear on my example, but I wish to use *merge *inside my
> create-map function. Do you think I should bind my hash-map to a let
> variable first and then apply merge, or do you have another proposal? What
> i mean is this:
>
> (defn create-key-value [value]
>
> (when (some-condition-true) {:extra-key value))
>
>
> (defn create-map []
>> (let [my-map {:foo "a" :bar "b"}]
>> (merge my-map (create-key-value "some-value")))
>
>
> Is the above "clojurish" or is there a better way? For example if the
> my-map was a big hash-map, and not with just two pairs, wouldn't it be ugly
> with the above way? or..it's just fine and no better way is possible?
>
> Ryan
>
> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
> (kotarak) wrote:
>>
>> Hi,
>>
>> merge works with nil. So (merge (create-map) (create-key-value
>> "some-value")) should work as you intend with the functions as they are
>> defined now.
>>
>> Kind regards
>> Meikel
>>
>> --
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Re: Creating a hash-map with conditional keys
Another alternative way, added in Clojure 1.5, can be nice if you have a
lot of conditionally-added key-value pairs:
(defn create-map []
> (cond-> {:base :map}
> (pred1) (assoc :extra-key1 value)
> (pred2) (assoc :extra-key2 value)
> (pred3) (assoc :extra-key3 value)
> (pred4) (assoc :extra-key4 value)))
On Thu, Feb 21, 2013 at 7:41 AM, Alex Baranosky <
alexander.barano...@gmail.com> wrote:
> I'd often just write it like this:
>
> (defn create-map []
>> (merge {:foo "a"
>>:bar "b"
>>... many more keys}
>> (when (some-condition-true)
>> {:extra-key value)))
>
>
> Alex
>
>
> On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
>
>> Thanks Meikel for your reply.
>>
>> It wasn't clear on my example, but I wish to use *merge *inside my
>> create-map function. Do you think I should bind my hash-map to a let
>> variable first and then apply merge, or do you have another proposal? What
>> i mean is this:
>>
>> (defn create-key-value [value]
>>
>> (when (some-condition-true) {:extra-key value))
>>
>>
>> (defn create-map []
>>> (let [my-map {:foo "a" :bar "b"}]
>>> (merge my-map (create-key-value "some-value")))
>>
>>
>> Is the above "clojurish" or is there a better way? For example if the
>> my-map was a big hash-map, and not with just two pairs, wouldn't it be ugly
>> with the above way? or..it's just fine and no better way is possible?
>>
>> Ryan
>>
>> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
>> (kotarak) wrote:
>>>
>>> Hi,
>>>
>>> merge works with nil. So (merge (create-map) (create-key-value
>>> "some-value")) should work as you intend with the functions as they are
>>> defined now.
>>>
>>> Kind regards
>>> Meikel
>>>
>>> --
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>>
>>
>
>
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Re: Creating a hash-map with conditional keys
Thanks for your input Alex.
Do you think a macro would be appropriate if I use this more than once in
my code?
Ryan
On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex Baranosky wrote:
>
> I'd often just write it like this:
>
> (defn create-map []
>> (merge {:foo "a"
>>:bar "b"
>>... many more keys}
>> (when (some-condition-true)
>> {:extra-key value)))
>
>
> Alex
>
> On Thu, Feb 21, 2013 at 7:27 AM, Ryan >wrote:
>
>> Thanks Meikel for your reply.
>>
>> It wasn't clear on my example, but I wish to use *merge *inside my
>> create-map function. Do you think I should bind my hash-map to a let
>> variable first and then apply merge, or do you have another proposal? What
>> i mean is this:
>>
>> (defn create-key-value [value]
>>
>> (when (some-condition-true) {:extra-key value))
>>
>>
>> (defn create-map []
>>> (let [my-map {:foo "a" :bar "b"}]
>>> (merge my-map (create-key-value "some-value")))
>>
>>
>> Is the above "clojurish" or is there a better way? For example if the
>> my-map was a big hash-map, and not with just two pairs, wouldn't it be ugly
>> with the above way? or..it's just fine and no better way is possible?
>>
>> Ryan
>>
>> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
>> (kotarak) wrote:
>>>
>>> Hi,
>>>
>>> merge works with nil. So (merge (create-map) (create-key-value
>>> "some-value")) should work as you intend with the functions as they are
>>> defined now.
>>>
>>> Kind regards
>>> Meikel
>>>
>>> --
>> --
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>> your first post.
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>>
>>
>
>
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Re: Creating a hash-map with conditional keys
A function could be appropriate, but a macro not appropriate, since
everything you need here can be done with using macros.
On Feb 21, 2013 7:53 AM, "Ryan" wrote:
> Thanks for your input Alex.
>
> Do you think a macro would be appropriate if I use this more than once in
> my code?
>
> Ryan
>
> On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex Baranosky wrote:
>>
>> I'd often just write it like this:
>>
>> (defn create-map []
>>> (merge {:foo "a"
>>>:bar "b"
>>>... many more keys}
>>> (when (some-condition-true)
>>> {:extra-key value)))
>>
>>
>> Alex
>>
>> On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
>>
>>> Thanks Meikel for your reply.
>>>
>>> It wasn't clear on my example, but I wish to use *merge *inside my
>>> create-map function. Do you think I should bind my hash-map to a let
>>> variable first and then apply merge, or do you have another proposal? What
>>> i mean is this:
>>>
>>> (defn create-key-value [value]
>>>
>>> (when (some-condition-true) {:extra-key value))
>>>
>>>
>>> (defn create-map []
(let [my-map {:foo "a" :bar "b"}]
(merge my-map (create-key-value "some-value")))
>>>
>>>
>>> Is the above "clojurish" or is there a better way? For example if the
>>> my-map was a big hash-map, and not with just two pairs, wouldn't it be ugly
>>> with the above way? or..it's just fine and no better way is possible?
>>>
>>> Ryan
>>>
>>> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
>>> (kotarak) wrote:
Hi,
merge works with nil. So (merge (create-map) (create-key-value
"some-value")) should work as you intend with the functions as they are
defined now.
Kind regards
Meikel
--
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>>> .
>>>
>>>
>>>
>>
>> --
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Re: Creating a hash-map with conditional keys
I got confused a bit with the reason that a macro would not be appropriate
for this case. Can you please explain again?
Ryan
On Thursday, February 21, 2013 7:05:11 PM UTC+2, Alex Baranosky wrote:
>
> A function could be appropriate, but a macro not appropriate, since
> everything you need here can be done with using macros.
> On Feb 21, 2013 7:53 AM, "Ryan" > wrote:
>
>> Thanks for your input Alex.
>>
>> Do you think a macro would be appropriate if I use this more than once in
>> my code?
>>
>> Ryan
>>
>> On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex Baranosky wrote:
>>>
>>> I'd often just write it like this:
>>>
>>> (defn create-map []
(merge {:foo "a"
:bar "b"
... many more keys}
(when (some-condition-true)
{:extra-key value)))
>>>
>>>
>>> Alex
>>>
>>> On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
>>>
Thanks Meikel for your reply.
It wasn't clear on my example, but I wish to use *merge *inside my
create-map function. Do you think I should bind my hash-map to a let
variable first and then apply merge, or do you have another proposal? What
i mean is this:
(defn create-key-value [value]
(when (some-condition-true) {:extra-key value))
(defn create-map []
> (let [my-map {:foo "a" :bar "b"}]
> (merge my-map (create-key-value "some-value")))
Is the above "clojurish" or is there a better way? For example if the
my-map was a big hash-map, and not with just two pairs, wouldn't it be
ugly
with the above way? or..it's just fine and no better way is possible?
Ryan
On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
(kotarak) wrote:
>
> Hi,
>
> merge works with nil. So (merge (create-map) (create-key-value
> "some-value")) should work as you intend with the functions as they are
> defined now.
>
> Kind regards
> Meikel
>
> --
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>>>
>>> --
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Re: Creating a hash-map with conditional keys
Macros should be avoided if you don't need them. Otherwise they
drastically reduce code readability. In this case you just have some
predicates and maps that need to be combined conditionally, so nothing
macros do is needed. The real question here is why you would need a macro?
Macros usage is, to me, a question of need, meaning I need to convince
myself that you need it or I wouldn't sacrifice code readability for it.
Things macros are good for:
- delayed code evaluation
- DSL creation
- moving computation to compile time (comes up occasionally)
- other metaprogramming, which I usually only consider worth it if it
reduces duplication enough
Alex
On Thu, Feb 21, 2013 at 9:11 AM, Ryan wrote:
> I got confused a bit with the reason that a macro would not be appropriate
> for this case. Can you please explain again?
>
> Ryan
>
>
> On Thursday, February 21, 2013 7:05:11 PM UTC+2, Alex Baranosky wrote:
>
>> A function could be appropriate, but a macro not appropriate, since
>> everything you need here can be done with using macros.
>> On Feb 21, 2013 7:53 AM, "Ryan" wrote:
>>
>>> Thanks for your input Alex.
>>>
>>> Do you think a macro would be appropriate if I use this more than once
>>> in my code?
>>>
>>> Ryan
>>>
>>> On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex Baranosky wrote:
I'd often just write it like this:
(defn create-map []
> (merge {:foo "a"
>:bar "b"
>... many more keys}
> (when (some-condition-true)
> {:extra-key value)))
Alex
On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
> Thanks Meikel for your reply.
>
> It wasn't clear on my example, but I wish to use *merge *inside my
> create-map function. Do you think I should bind my hash-map to a let
> variable first and then apply merge, or do you have another proposal? What
> i mean is this:
>
> (defn create-key-value [value]
>
> (when (some-condition-true) {:extra-key value))
>
>
> (defn create-map []
>> (let [my-map {:foo "a" :bar "b"}]
>> (merge my-map (create-key-value "some-value")))
>
>
> Is the above "clojurish" or is there a better way? For example if the
> my-map was a big hash-map, and not with just two pairs, wouldn't it be
> ugly
> with the above way? or..it's just fine and no better way is possible?
>
> Ryan
>
> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
> (kotarak) wrote:
>>
>> Hi,
>>
>> merge works with nil. So (merge (create-map) (create-key-value
>> "some-value")) should work as you intend with the functions as they are
>> defined now.
>>
>> Kind regards
>> Meikel
>>
>> --
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Re: Creating a hash-map with conditional keys
I think Alex is trying to say that a macro is almost never appropriate
when a first-class function would do...therefore, there is no good
reason for carrying the complexity of macros all over your code, given
that in your case they do nothing special (like postponed evaluation)
and can be replaced by functions.
Jim
On 21/02/13 17:11, Ryan wrote:
I got confused a bit with the reason that a macro would not be
appropriate for this case. Can you please explain again?
Ryan
On Thursday, February 21, 2013 7:05:11 PM UTC+2, Alex Baranosky wrote:
A function could be appropriate, but a macro not appropriate,
since everything you need here can be done with using macros.
On Feb 21, 2013 7:53 AM, "Ryan" >
wrote:
Thanks for your input Alex.
Do you think a macro would be appropriate if I use this more
than once in my code?
Ryan
On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex
Baranosky wrote:
I'd often just write it like this:
(defn create-map []
(merge {:foo "a"
:bar "b"
... many more keys}
(when (some-condition-true)
{:extra-key value)))
Alex
On Thu, Feb 21, 2013 at 7:27 AM, Ryan
wrote:
Thanks Meikel for your reply.
It wasn't clear on my example, but I wish to use
*merge *inside my create-map function. Do you think I
should bind my hash-map to a let variable first and
then apply merge, or do you have another proposal?
What i mean is this:
(defn create-key-value [value]
(when (some-condition-true) {:extra-key value))
(defn create-map []
(let [my-map {:foo "a" :bar "b"}]
(merge my-map (create-key-value "some-value")))
Is the above "clojurish" or is there a better way? For
example if the my-map was a big hash-map, and not with
just two pairs, wouldn't it be ugly with the above
way? or..it's just fine and no better way is possible?
Ryan
On Thursday, February 21, 2013 5:02:21 PM UTC+2,
Meikel Brandmeyer (kotarak) wrote:
Hi,
merge works with nil. So (merge (create-map)
(create-key-value "some-value")) should work as
you intend with the functions as they are defined now.
Kind regards
Meikel
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Re: Creating a hash-map with conditional keys
Thank you both for your answers
Regards,
Ryan
On Thursday, February 21, 2013 7:43:05 PM UTC+2, Jim foo.bar wrote:
>
> I think Alex is trying to say that a macro is almost never appropriate
> when a first-class function would do...therefore, there is no good reason
> for carrying the complexity of macros all over your code, given that in
> your case they do nothing special (like postponed evaluation) and can be
> replaced by functions.
>
> Jim
>
>
> On 21/02/13 17:11, Ryan wrote:
>
> I got confused a bit with the reason that a macro would not be appropriate
> for this case. Can you please explain again?
>
> Ryan
>
> On Thursday, February 21, 2013 7:05:11 PM UTC+2, Alex Baranosky wrote:
>>
>> A function could be appropriate, but a macro not appropriate, since
>> everything you need here can be done with using macros.
>> On Feb 21, 2013 7:53 AM, "Ryan" wrote:
>>
>>> Thanks for your input Alex.
>>>
>>> Do you think a macro would be appropriate if I use this more than once
>>> in my code?
>>>
>>> Ryan
>>>
>>> On Thursday, February 21, 2013 5:41:49 PM UTC+2, Alex Baranosky wrote:
I'd often just write it like this:
(defn create-map []
> (merge {:foo "a"
>:bar "b"
>... many more keys}
> (when (some-condition-true)
> {:extra-key value)))
Alex
On Thu, Feb 21, 2013 at 7:27 AM, Ryan wrote:
> Thanks Meikel for your reply.
>
> It wasn't clear on my example, but I wish to use *merge *inside my
> create-map function. Do you think I should bind my hash-map to a let
> variable first and then apply merge, or do you have another proposal?
> What
> i mean is this:
>
> (defn create-key-value [value]
>
> (when (some-condition-true) {:extra-key value))
>
>
> (defn create-map []
>> (let [my-map {:foo "a" :bar "b"}]
>> (merge my-map (create-key-value "some-value")))
>
>
> Is the above "clojurish" or is there a better way? For example if
> the my-map was a big hash-map, and not with just two pairs, wouldn't it
> be
> ugly with the above way? or..it's just fine and no better way is possible?
>
> Ryan
>
> On Thursday, February 21, 2013 5:02:21 PM UTC+2, Meikel Brandmeyer
> (kotarak) wrote:
>>
>> Hi,
>>
>> merge works with nil. So (merge (create-map) (create-key-value
>> "some-value")) should work as you intend with the functions as they are
>> defined now.
>>
>> Kind regards
>> Meikel
>>
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