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<div class="moz-cite-prefix">A straight-forward way to provide a
maps merge function based on the dict documentation is:<br>
<br>
maps_update(K, F, V0, Map) -><br>
try maps:get(K, Map) of<br>
V1 -><br>
maps:put(K, F(V1), Map)<br>
catch<br>
error:{badkey, K} -><br>
maps:put(K, V0, Map)<br>
end.<br>
<br>
maps_merge(Fun, Map1, Map2) -><br>
maps:fold(fun (K, V1, Map) -><br>
maps_update(K, fun (V2) -> Fun(K, V1, V2)
end, V1, Map)<br>
end, Map2, Map1).<br>
<br>
Not sure about the speed compared to the code below, but both
results should be the same if everything is working properly.<br>
<br>
On 08/26/2015 11:44 AM, Ivan Uemlianin wrote:<br>
</div>
<blockquote cite="mid:55DE091A.5090104@llaisdy.com" type="cite">
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
Dear Alexander, Hynek<br>
<br>
That is a *lot* faster! :D <br>
<br>
Thanks very much both.<br>
<br>
Ivan<br>
<br>
<br>
<div class="moz-cite-prefix">On 08/26/15 10:38, Ivan Uemlianin
wrote:<br>
</div>
<blockquote cite="mid:55DD8933.10001@llaisdy.com" type="cite">
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http-equiv="Content-Type">
Oh yes of course that's better. Thanks<br>
<br>
Ivan<br>
<br>
<br>
<div class="moz-cite-prefix">On 26/08/2015 10:32, Hynek Vychodil
wrote:<br>
</div>
<blockquote
cite="mid:CAL_wnpdX2F9vtRd_YGjmMTscwhRcBD830+Mhfg+Zd-reYvKCSg@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>I would consider:</div>
<div><br>
</div>
<div>merge_ap(F, [Head | Tail]) -></div>
<div> lists:foldl(fun(Y, X) -></div>
<div> <a moz-do-not-send="true"
class="moz-txt-link-freetext" href="maps:merge%28X">maps:merge(X</a>,
<a moz-do-not-send="true" class="moz-txt-link-freetext"
href="maps:map%28fun%28Key">maps:map(fun(Key</a>, Value)
-></div>
<div>
case <a moz-do-not-send="true"
class="moz-txt-link-freetext" href="maps:find%28Key">maps:find(Key</a>,
X) of</div>
<div>
{ok, V} -> F(Key, V, Value);</div>
<div>
error -> Value</div>
<div>
end<br>
</div>
<div> end,</div>
<div> Y))</div>
<div> end,</div>
<div> Head,</div>
<div> Tail).</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Aug 26, 2015 at 10:45 AM,
Ivan Uemlianin <span dir="ltr"><<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px
0px
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> Dear Alexander<br>
<br>
Thanks! That looks excellent!<br>
<br>
I notice that your function F is different from the
<a moz-do-not-send="true"
class="moz-txt-link-freetext" href="dict:merge/3">dict:merge/3</a>
function: instead of taking a key and the two
values, is takes two values, defaulting the first to
0. <br>
<br>
I've put my case clause into your framework:<br>
<br>
merge_ap(F, [Head | Tail]) -><span class=""><br>
lists:foldl(fun(Y, X) -><br>
<a moz-do-not-send="true">maps:merge(X</a>,
<a moz-do-not-send="true">maps:map(fun(Key</a>,
Value) -><br>
</span>
case <a moz-do-not-send="true">maps:is_key(Key</a>,
X) of<br>
false -><br>
Value;<br>
true -><br>
F(Key, Value, <a moz-do-not-send="true">maps:get(Key</a>,
X))<br>
end<span class=""><br>
end,<br>
Y))<br>
end,<br>
Head,<br>
Tail).<br>
<br>
</span> This has desired behaviour, and will
probably still perform well. Using lists:foldl is a
brilliant idea.<br>
<br>
Best wishes<span class=""><font color="#888888"><br>
<br>
Ivan</font></span>
<div>
<div class="h5"><br>
<br>
<br>
<div>On 26/08/2015 09:16, Alexander Petrovsky
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hi!
<div><br>
</div>
<div>I've make some little benchmarks, and
noticed that the most effective way is:</div>
<div><br>
</div>
<div>merge(F, [Head | Tail]) -></div>
<div> lists:foldl(fun(Y, X) -> <a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:merge%28X">maps:merge(X</a>,
<a moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:map%28fun%28Key">maps:map(fun(Key</a>,
Value) -> F(<a moz-do-not-send="true">maps:get(Key</a>,
X, 0), Value) end, Y)) end, Head, Tail).</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2015-08-23 20:05
GMT+03:00 Ivan Uemlianin <span dir="ltr"><<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a>></span>:<br>
<blockquote class="gmail_quote"
style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Dear
All<br>
<br>
The maps module does not have a merge/3
like <a moz-do-not-send="true">dict:merge/3</a>,
which calls a function fun(Key, Val1,
Val2) when both dicts have the same
key. From the documentation, "If a key
occurs in both dictionaries then Fun is
called with the key and both values to
return a new value."<br>
<br>
The dict documentation says that <a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="dict:merge/3">dict:merge/3</a>
is faster than an equivalent implemented
in erlang.<br>
<br>
<a moz-do-not-send="true"
href="http://www.erlang.org/doc/man/dict.html#merge-3"
rel="noreferrer" target="_blank">http://www.erlang.org/doc/man/dict.html#merge-3</a><br>
<br>
Why does the maps module not have a
similar merge/3? Is it because writing
our own erlang implementation is at fast
as it gets?<br>
<br>
Below is an implementation which seems
to work. Can it be made faster?<br>
<br>
<br>
merge_maps(Fun, M1, M2) -><br>
<a moz-do-not-send="true">maps:fold(fun(K</a>,
V1, Acc) -><br>
case <a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:is_key%28K">maps:is_key(K</a>,
Acc) of<br>
false -><br>
<a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:put%28K">maps:put(K</a>,
V1, Acc);<br>
true -><br>
V2 = <a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:get%28K">maps:get(K</a>,
Acc),<br>
<a
moz-do-not-send="true"
class="moz-txt-link-freetext"
href="maps:put%28K">maps:put(K</a>,
Fun(K, V1, V2), Acc)<br>
end<br>
end,<br>
M1,<br>
M2).<br>
<br>
merge_maps_test() -><br>
merge_maps(fun(_K, V1, V2) -> V1
+ V2 end,<br>
#{a => 1, b => 2, c
=> 3},<br>
#{b => 2, c => 3, d
=> 4}) =:=<br>
#{a => 1, b => 4, c =>
6, d => 4}.<br>
<br>
<br>
With thanks and best wishes<br>
<br>
Ivan<br>
<br>
-- <br>
============================================================<br>
Ivan A. Uemlianin PhD<br>
Llaisdy<br>
Speech Technology Research and
Development<br>
<br>
<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a><br>
@llaisdy<br>
<a
moz-do-not-send="true"
href="http://llaisdy.wordpress.com"
rel="noreferrer" target="_blank">llaisdy.wordpress.com</a><br>
<a moz-do-not-send="true"
href="http://github.com/llaisdy"
rel="noreferrer" target="_blank">github.com/llaisdy</a><br>
<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="http://www.linkedin.com/in/ivanuemlianin">www.linkedin.com/in/ivanuemlianin</a><br>
<br>
festina lente<br>
============================================================<br>
<br>
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</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div>
<div dir="ltr">Петровский Александр /
Alexander Petrovsky,<br>
<br>
Skype: askjuise<br>
<div>Phone: +7 914 8 820 815
<div><br>
</div>
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Ivan A. Uemlianin PhD
Llaisdy
Speech Technology Research and Development
<a moz-do-not-send="true" href="mailto:ivan@llaisdy.com" target="_blank">ivan@llaisdy.com</a>
@llaisdy
<a moz-do-not-send="true" href="http://llaisdy.wordpress.com" target="_blank">llaisdy.wordpress.com</a>
<a moz-do-not-send="true" href="http://github.com/llaisdy" target="_blank">github.com/llaisdy</a>
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festina lente
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============================================================
Ivan A. Uemlianin PhD
Llaisdy
Speech Technology Research and Development
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a>
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Ivan A. Uemlianin PhD
Llaisdy
Speech Technology Research and Development
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a>
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