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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>It looks similar to the problem that I had
– the code worked only when subresult was evaluated.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a
href="http://www.erlang.org/pipermail/erlang-questions/2008-January/032389.html">http://www.erlang.org/pipermail/erlang-questions/2008-January/032389.html</a><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>maybe the patch here helps?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>http://www.erlang.org/pipermail/erlang-questions/2008-January/032410.html<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
erlang-questions-bounces@erlang.org
[mailto:erlang-questions-bounces@erlang.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Adam Bozanich<br>
<b><span style='font-weight:bold'>Sent:</span></b> 11. helmikuuta 2008 5:10<br>
<b><span style='font-weight:bold'>To:</span></b> erlang-questions@erlang.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [erlang-questions] qlc
expression help.</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Hi all,<br>
<br>
I'm having trouble creating a qlc expression which does what I want. I'm
basically trying to create a filter for QH1 with a predicate that depends on
QH2. <br>
In the example below, test2/0 gives me the result I'm looking for, but it
requires the second QH to be eval'd. I'd like the expression to look like
what's in the test1/0 function. Any suggestions?<br>
<br>
Thanks,<br>
-Adam<br>
<br>
session:<br>
8> test_qlc:test2().<br>
[{1,6,7},{2,8,9}]<br>
9> test_qlc:test1().<br>
[{1,4,5},<br>
{1,2,3},<br>
{1,6,7},<br>
{1,6,7},<br>
{2,4,5},<br>
{2,2,3},<br>
{2,8,9},<br>
{2,8,9},<br>
{3,4,5},<br>
{3,2,3}]<br>
<br>
code:<br>
<br>
-module(test_qlc).<br>
-include_lib("stdlib/include/qlc.hrl").<br>
-export([test1/0,test2/0,handroll/0]).<br>
<br>
-define(DB,[<br>
{1,4,5},{1,2,3},{1,6,7},<br>
{2,4,5},{2,2,3},{2,8,9},<br>
{3,4,5},{3,2,3}<br>
]).<br>
-define(OBJ,[{2,3},{4,5}]).<br>
<br>
test1() -><br>
qlc:eval(qlc:q([ {O1,C1,V1} ||<br>
{O1,C1,V1} <- ?DB,<br>
{C2,V2} <- ?OBJ,<br>
C1 /= C2,<br>
V1 /= V2])).<br>
test2() -><br>
qlc:eval(qlc:q([ {O1,C1,V1} ||<br>
{O1,C1,V1} <- ?DB,<br>
lists:member({C1,V1},?OBJ) == false ])).<br>
<br>
handroll() -><br>
S = mkset(?DB),<br>
O = mkobj(?OBJ),<br>
to_table(difference(O,related(O,S))).<br>
<br>
related(S1,D) -><br>
dict:filter(fun(_,S2) -><br>
sets:is_subset(S1,S2)<br>
end,D).<br>
<br>
difference(S1,D) -><br>
dict:filter(fun(_,S2) -><br>
sets:size(S2) > 0<br>
end,<br>
dict:map(fun(_,S2) -><br>
sets:subtract(S2,S1)<br>
end,D)).<br>
<br>
to_table(D) -><br>
lists:flatmap(fun({K,V}) -><br>
lists:map(fun({X,Y}) -><br>
{K,X,Y}<br>
end,<br>
sets:to_list(V))<br>
end,<br>
dict:to_list(D)).<br>
<br>
mkset(DB) -><br>
dict:map(fun(_,V) -><br>
sets:from_list(V)<br>
end,<br>
lists:foldl(fun({O,C,V},Acc) -><br>
dict:append(O,{C,V},Acc)<br>
end,<br>
dict:new(),DB)).<br>
<br>
mkobj(OBJ) -><br>
sets:from_list(OBJ).<o:p></o:p></span></font></p>
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