On Wed, Feb 23, 2011 at 11:55 AM, Benny Tsai <benny.t...@gmail.com> wrote:
> My guess is that Clojure's fmap behaves that way because it is modeled
> after Haskell's fmap
Hmm, I thought it might be a Haskell thing.
> To pass both keys and values to your transforming function, I think
> Alan's idea of using 'walk' is the best:
>
> (use '[clojure.walk :only (walk)])
>
> (def my-map {:first "john" :last "smith" :age 25})
>
> (defn my-fn [[key value]]
> (if (string? value)
> [key (.toUpperCase value)]
> [key value]))
>
> user=> (walk my-fn identity my-map)
> {:first "JOHN", :last "SMITH", :age 25}
That looks pretty nice. I'll give that a shot, thanks.
>
> On Feb 23, 6:27 am, Chris Maier <christopher.ma...@gmail.com> wrote:
>> Can anybody explain why fmap, when operating on an IPersistentMap,
>> only passes the function the value of the map entry, instead of the
>> entire map entry (i.e., the key and value pair)? It seems a bit odd
>> in that all the other implementations of fmap operate on the entire
>> item in the sequence. Also, I can imagine cases where you'd want to
>> do some map transformation that also depends on the key (do something
>> for entries A, B, and C, but something else for entries X, Y, and Z).
>>
>> I suppose I could use remove-method and then write my own fmap
>> implementation for IPersistentMap. I'm curious about the design,
>> though.
>>
>> Thanks,
>> Chris
>>
>>
>>
>>
>>
>>
>>
>> On Tue, Feb 22, 2011 at 6:56 PM, Benny Tsai <benny.t...@gmail.com> wrote:
>> > There is fmap from clojure.contrib.generic.functor, which expects a
>> > function of arity 1, for just the value:
>>
>> > (use 'clojure.contrib.generic.functor)
>> > (require '[clojure.string :as str])
>>
>> > (def my-map {:first "john" :last "smith" :age 25})
>>
>> > (defn my-fn [value]
>> > (if (string? value)
>> > (str/upper-case value)
>> > value))
>>
>> > user=> (fmap my-fn my-map)
>> > {:first "JOHN", :last "SMITH", :age 25}
>>
>> > On Feb 22, 4:23 pm, rob levy <r.p.l...@gmail.com> wrote:
>> >> The usual intuitive options for this are reduce, zipmap, or into. You can
>> >> also write a lazily recursive solution. I wonder why there's no function
>> >> in
>> >> core that lazily re-constructs the map with the results of the function?
>> >> It
>> >> seems to have been discussed on the list at least once or twice. It seems
>> >> like there would have to be two versions of it, one expecting a function
>> >> with an arity of one (for just the value) and another expecting an arity
>> >> of
>> >> two (key and value).
>>
>> >> On Mon, Feb 21, 2011 at 10:08 PM, yair <yair....@gmail.com> wrote:
>> >> > I'm hoping this is a dumb question and I've missed something obvious.
>> >> > I have a map with various key-value pairs and I want to transform some
>> >> > of the values, e.g.
>>
>> >> > (def mymap {:first "john" :last "smith" :age 25}) and say I want to
>> >> > change the strings to be upper case.
>> >> > Right now all I can think of doing is using reduce and passing in an
>> >> > empty map and the re-associating each key with the (possibly)
>> >> > transformed value. Is there something like the map function that
>> >> > takes two parameters, one a function that receives a pair and returns
>> >> > a new pair, and the other a map, and returns a map that's
>> >> > reconstituted from those pairs?
>>
>> >> > Thanks
>>
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