[erlang-questions] searching in an ETS table for substring

[Hynek Vychodil]

On Sat, Feb 11, 2012 at 8:25 PM, Hynek Vychodil <hynek@REDACTED> wrote:
> This approach seems work as well:
>
> ets:select(T, [{{"er"++'$1','_'}, [], ["er"++'$1']}]).
> ["erring","ericsson","erlang"]

and dynamic creation works as well

Prefix = "er", ets:select(T, [{{Prefix++'$1','_'}, [], [Prefix++'$1']}]).
["erring","ericsson","erlang"]

>
> On Sat, Feb 11, 2012 at 4:19 PM, Steve Vinoski <vinoski@REDACTED> wrote:
>> On Sat, Feb 11, 2012 at 8:28 AM, Avinash Dhumane <avinash@REDACTED> wrote:
>>> I am learning Erlang, and I must be doing something wrong here; please
>>> correct me! Thanks.
>>>
>>> avinash@REDACTED:~$ erl
>>> Erlang R14B02 (erts-5.8.3) [source] [smp:2:2] [rq:2] [async-threads:0]
>>> [kernel-poll:false]
>>>
>>> Eshell V5.8.3  (abort with ^G)
>>> 1>  T=ets:new(test, [set]).
>>> 16400
>>> 2>  ets:insert(T, {"erlang", 1}).
>>> true
>>> 3>  ets:insert(T, {"ericsson", 2}).
>>> true
>>> 4> ets:insert(T, {"erring", 3}).
>>> true
>>> 5>
>>> 5> ets:insert(T, {"ejection", 4}).
>>> true
>>> 6>  ets:insert(T, {"emersion", 5}).
>>> true
>>> 7> ets:select(T, [{{'$1', '_'}, [], ['$$']}]).
>>> [["erring"],
>>>  ["emersion"],
>>>  ["ericsson"],
>>>  ["erlang"],
>>>  ["ejection"]]
>>> 8> ets:select(T, [{{'$1', '_'}, [{'==', '$1', "er"++'_'}], ['$$']}]).
>>> []
>>> 9> ets:select(T, [{{'$1', '_'}, [{'=:=', '$1', "er"++'_'}], ['$$']}]).
>>> []
>>> 10> ets:select(T, [{{'$1', '_'}, [{'=', '$1', "er"++'_'}], ['$$']}]).
>>> ** exception error: bad argument
>>>      in function  ets:select/2
>>>         called as ets:select(16400,
>>>
>>> [{{'$1','_'},[{'=','$1',[101,114|'_']}],['$$']}])
>>> 11>
>>
>> One approach:
>>
>> 1> ets:select(T, [{{"er"++'_','_'}, [], ['$_']}]).
>> [{"erring",3},{"ericsson",2},{"erlang",1}]
>>
>> But note this returns entire objects, not just keys. Still, I think
>> that's what Martin might have wanted, since it matches what his
>> original SQL select example would do.
>>
>> Another approach, fetching just the keys:
>>
>> 2> MS = ets:fun2ms(fun({K,_}) when is_list(K), hd(K) =:= $e, hd(tl(K))
>> =:= $r -> K end).
>> [{{'$1','_'},
>>  [{is_list,'$1'},
>>   {'=:=',{hd,'$1'},101},
>>   {'=:=',{hd,{tl,'$1'}},114}],
>>  ['$1']}]
>> 3> ets:select(T, MS).
>> ["erring","ericsson","erlang"]
>>
>> This approach can work OK if you're matching a prefix of just 2 or 3
>> characters, but could get tedious beyond that.
>>
>> --steve
>> _______________________________________________
>> erlang-questions mailing list
>> erlang-questions@REDACTED
>> http://erlang.org/mailman/listinfo/erlang-questions
>
>
>
> --
> Hynek Vychodil
> BI consultant
>
> GoodData
> náměstí 28. října 1104/17, 602 00, Brno - Černá Pole
> Office:   +420 530 50 7704
> E-mail:  hynek@REDACTED
> Web:     www.gooddata.com



-- 
Hynek Vychodil
BI consultant

GoodData
náměstí 28. října 1104/17, 602 00, Brno - Černá Pole
Office:   +420 530 50 7704
E-mail:  hynek@REDACTED
Web:     www.gooddata.com