Hey, just to share, I came up with this code, which seem quite ok to me,
Feels like I already understand something, do i,
Have a nice day, Frank
(loop
[a '(1 2 3 4)
b '(1 3)
out ()]
(cond
(and (empty? a)(empty? b)) out
(empty? a) (recur a (rest b) (conj out [nil (first
b)]))
(empty? b) (recur (rest a) b (conj out [(first a)
nil]))
:else (let
[fa (first a)
fb (first b)
cmp (compare fa fb)]
(cond
(= 0 cmp) (recur (rest a) (rest b) (conj out [fa fb]))
(> 0 cmp) (recur (rest a) b (conj out [fa nil]))
:else (recur a (rest b) (conj out [nil fb]))))))
Am Montag, 10. März 2014 09:26:14 UTC+1 schrieb Frank Behrens:
>
> Thanks for your suggestions.
> a for loop has to do 100.000 * 300.000 compares
> Storing the database table into a 300.000 element hash, would be a memory
> penalty I want to avoid.
>
> I'm quite shure that assential part of the solution is a function to
> iterate through both list at once,
> spitting out pairs of values according to compare
>
> (merge-sortedlists
> '(1 2 3)
> '( 2 4))
> => ([1 nil] [2 2] [3 nil] [nil 4])
>
> Seems quite doable.
> Try to implement now.
>
> Frank
>
>
> Am Montag, 10. März 2014 01:23:57 UTC+1 schrieb frye:
>>
>> Hmm, the *for* comprehension yields a lazy sequence of results. So the
>> penalty should only occur when one starts to use / evaluate the result.
>> Using maps is a good idea. But I think you'll have to use another algorithm
>> (not *for*) to get the random access you seek.
>>
>> Frank could try a *clojure.set/intersection* to find common keys between
>> the lists. then *order* and *map* / *merge* the 2 lists.
>>
>> Beyond that, I can't see a scenario where some iteration won't have to
>> search the space for matching keys (which I think
>> *clojure.set/intersection* does). A fair point all the same.
>>
>>
>> Tim Washington
>> Interruptsoftware.com <http://interruptsoftware.com>
>>
>>
>> On Sun, Mar 9, 2014 at 12:13 PM, Moritz Ulrich <mor...@tarn-vedra.de>wrote:
>>
>>> I think it would be more efficient to read one of the inputs into a
>>> map for random access instead of iterating it every time.
>>>
>>> On Sun, Mar 9, 2014 at 4:48 PM, Timothy Washington <twas...@gmail.com>
>>> wrote:
>>> > Hey Frank,
>>> >
>>> > Try opening up a repl, and running this for comprehension.
>>> >
>>> > (def user_textfile [[:id1 {:name 'Frank'}] [:id3 {:name 'Tim'}]])
>>> > (def user_database [[:id1 {:age 38}] [:id2 {:age 27}] [:id3 {:age 18}]
>>> [:id4
>>> > {:age 60}]])
>>> >
>>> > (for [i user_textfile
>>> > j user_database
>>> > :when (= (first i) (first j))]
>>> > {(first i) (merge (second i) (second j))})
>>> >
>>> > ({:id1 {:age 38, :name Frank'}} {:id3 {:age 18, :name Tim'}}) ;;
>>> result
>>> > from repl
>>> >
>>> >
>>> >
>>> > Hth
>>> >
>>> > Tim Washington
>>> > Interruptsoftware.com
>>> >
>>> >
>>> > On Sun, Mar 9, 2014 at 5:33 AM, Frank Behrens <fbeh...@gmail.com>
>>> wrote:
>>> >>
>>> >> Hi,
>>> >>
>>> >> i'm investigating if clojure can be used to solve the challenges and
>>> >> problems we have at my day job better than ruby or powershell. A very
>>> common
>>> >> use case is validating data from different systems against some
>>> criteria. i
>>> >> believe clojure can be our silver bullet, but before that, it seems
>>> to be
>>> >> required to wrap my head around it.
>>> >>
>>> >> So I am starting in the first level with the challenge to validate
>>> some
>>> >> data from the user database against our active directory.
>>> >>
>>> >> I already have all the parts to make it work: Which is to make a hash
>>> by
>>> >> user_id from the database table, export a textfile from AD, each line
>>> >> representing a user, parse it, merge the information from the
>>> >> user_table_hash, and voila.
>>> >>
>>> >> I did not finish to implement this. So I don't know if this naive
>>> approach
>>> >> will work with 400.000 records in the user database and 100.000 in the
>>> >> textfile.
>>> >> But I already think about how I could implement this in a more memory
>>> >> efficient way.
>>> >>
>>> >> So my simple question:
>>> >>
>>> >> I have user_textfile (100.000 records) which can be parsed into a
>>> >> unordered list of user-maps.
>>> >> I have user_table in the database(400.000 record) which I can query
>>> with
>>> >> order and gives me an ordered list of user-maps.
>>> >>
>>> >> So I would first order the user_textfile and then conj the user_table
>>> >> ordered list into it, while doing the database query.
>>> >> Is that approach right ? How would I then merge the two ordered lists
>>> like
>>> >> in the example below?
>>> >>
>>> >> (defn user_textfile
>>> >> ([:id1 {:name 'Frank'}]
>>> >> [:id3 {:name 'Tim'}]))
>>> >>
>>> >> (defn user_database
>>> >> ([:id1 {:age 38}]
>>> >> [:id2 {:age 27}]
>>> >> [:id3 {:age 18}]
>>> >> [:id4 {:age 60}]))
>>> >>
>>> >> (merge-sorted-lists user_database user_textfile)
>>> >> =>
>>> >> ([:id1 {:name 'Frank' :age 38}]
>>> >> [:id3 {:name 'Tim' :age 18}]))
>>> >>
>>> >> Any feedback is appreciated.
>>> >> Have a nice day,
>>> >> Frank
>>> >>
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