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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 class="moz-txt-link-freetext" href="maps:merge(X">maps:merge(X</a>, <a class="moz-txt-link-freetext" href="maps:map(fun(Key">maps:map(fun(Key</a>,
Value) -></div>
<div> case
<a class="moz-txt-link-freetext" href="maps:find(Key">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" href="mailto:ivan@llaisdy.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a></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"><a class="moz-txt-link-freetext" href="dict:merge/3">dict:merge/3</a></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"><a class="moz-txt-link-freetext" href="maps:merge(X">maps:merge(X</a></a>, <a
moz-do-not-send="true"><a class="moz-txt-link-freetext" href="maps:map(fun(Key">maps:map(fun(Key</a></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"
href="mailto:ivan@llaisdy.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a></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"><a class="moz-txt-link-freetext" href="dict:merge/3">dict:merge/3</a></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"><a class="moz-txt-link-freetext" href="maps:is_key(K">maps:is_key(K</a></a>,
Acc) of<br>
false -><br>
<a
moz-do-not-send="true"><a class="moz-txt-link-freetext" href="maps:put(K">maps:put(K</a></a>, V1,
Acc);<br>
true -><br>
V2 = <a
moz-do-not-send="true"><a class="moz-txt-link-freetext" href="maps:get(K">maps:get(K</a></a>,
Acc),<br>
<a
moz-do-not-send="true"><a class="moz-txt-link-freetext" href="maps:put(K">maps:put(K</a></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"
href="mailto:ivan@llaisdy.com"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a></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"
href="http://www.linkedin.com/in/ivanuemlianin"
rel="noreferrer" target="_blank"><a class="moz-txt-link-abbreviated" href="http://www.linkedin.com/in/ivanuemlianin">www.linkedin.com/in/ivanuemlianin</a></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>
</div>
</div>
</div>
</div>
</blockquote>
<br>
<pre cols="72">--
============================================================
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>
<a moz-do-not-send="true" href="http://www.linkedin.com/in/ivanuemlianin" target="_blank">www.linkedin.com/in/ivanuemlianin</a>
festina lente
============================================================ </pre>
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</blockquote>
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
============================================================
Ivan A. Uemlianin PhD
Llaisdy
Speech Technology Research and Development
<a class="moz-txt-link-abbreviated" href="mailto:ivan@llaisdy.com">ivan@llaisdy.com</a>
@llaisdy
llaisdy.wordpress.com
github.com/llaisdy
<a class="moz-txt-link-abbreviated" href="http://www.linkedin.com/in/ivanuemlianin">www.linkedin.com/in/ivanuemlianin</a>
festina lente
============================================================ </pre>
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