https://github.com/MichaelBlume/eval-speed
eval-speed.core=> (time-fn read-to-maps)
"Elapsed time: 5551.011069 msecs"
nil
eval-speed.core=> (time-fn read-to-maps-fn)
"Elapsed time: 5587.256991 msecs"
nil
eval-speed.core=> (time-fn read-to-maps-partial)
"Elapsed time: 5606.649172 msecs"
nil
eval-speed.core=> (time-fn read-to-maps-eval)
"Elapsed time: 2627.521592 msecs"
nil
Ben, I'd still like to understand exactly what work the CPU is doing in the
uneval'd version that it's skipping in the eval'd version. It seems like in
the generated bytecode there's going to be *some* concept of iterating
through the row in either case, if only as part of the destructuring
process.
On Friday, October 10, 2014 1:07:08 PM UTC-7, Ben wrote:
>
> I believe it's because the `mapper` function is just creating and
> returning a map literal. The "mapper" function in the evaled version is
> something like this:
>
> user> (def names '[n1 n2 n3 n4])
> #'user/names
> user> (def headers '[h1 h2 h3 h4])
> #'user/headers
> user> `(fn [[~@names]] ~(zipmap headers names))
> (clojure.core/fn [[n1 n2 n3 n4]] {h4 n4, h3 n3, h2 n2, h1 n1}) ;; just a
> map literal, whose keys are already known.
>
> Whereas in the first version, zipmap has to be called, iterating over
> headers and names each time.
>
> On Fri, Oct 10, 2014 at 1:04 PM, Sean Corfield <se...@corfield.org
> <javascript:>> wrote:
>
>> It may be more to do with the difference between `for` and `map`. How do
>> these versions compare in your benchmark:
>>
>> (defn read-to-maps-partial [rows]
>> (let [headers (->>
>> rows
>> first
>> (take-while (complement #{""}))
>> (map keyword))]
>> (map (partial zipmap headers) (rest rows))))
>>
>> (defn read-to-maps-fn [rows]
>> (let [headers (->>
>> rows
>> first
>> (take-while (complement #{""}))
>> (map keyword))
>> mapper (fn [row] (zipmap headers row))]
>> (map mapper (rest rows))))
>>
>> Sean
>>
>> On Oct 10, 2014, at 11:42 AM, Michael Blume <blume...@gmail.com
>> <javascript:>> wrote:
>> > So I'm reading a bunch of rows from a huge csv file and marshalling
>> those rows into maps using the first row as keys. I wrote the function two
>> ways: https://gist.github.com/MichaelBlume/c67d22df0ff9c225d956 and the
>> version with eval is twice as fast and I'm kind of curious about why.
>> Presumably the eval'd function still implicitly contains a list of keys,
>> it's still implicitly treating each row as a seq and walking it, so I'm
>> wondering what the seq-destructuring and the map literal are doing under
>> the hood that's faster.
>>
>>
>
>
> --
> Ben Wolfson
> "Human kind has used its intelligence to vary the flavour of drinks, which
> may be sweet, aromatic, fermented or spirit-based. ... Family and social
> life also offer numerous other occasions to consume drinks for pleasure."
> [Larousse, "Drink" entry]
>
>
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