<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> maps:merge(X, maps:map(fun(Key, Value) -></div><div> case maps:find(Key, 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 href="mailto:ivan@llaisdy.com" target="_blank">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>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>maps:merge(X</a>, <a>maps:map(fun(Key</a>, Value) -><br></span>
case
<a>maps:is_key(Key</a>, X) of<br>
false
-><br>
Value;<br>
true
-><br>
F(Key, Value, <a>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>maps:merge(X</a>,
<a>maps:map(fun(Key</a>, Value) -> F(<a>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 href="mailto:ivan@llaisdy.com" target="_blank">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>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>dict:merge/3</a> is faster than
an equivalent implemented in erlang.<br>
<br>
<a 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>maps:fold(fun(K</a>, V1, Acc) -><br>
case <a>maps:is_key(K</a>, Acc) of<br>
false -><br>
<a>maps:put(K</a>, V1, Acc);<br>
true -><br>
V2 = <a>maps:get(K</a>, Acc),<br>
<a>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 href="mailto:ivan@llaisdy.com" target="_blank">ivan@llaisdy.com</a><br>
@llaisdy<br>
<a href="http://llaisdy.wordpress.com" rel="noreferrer" target="_blank">llaisdy.wordpress.com</a><br>
<a href="http://github.com/llaisdy" rel="noreferrer" target="_blank">github.com/llaisdy</a><br>
<a href="http://www.linkedin.com/in/ivanuemlianin" rel="noreferrer" target="_blank">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>
</div>
</div>
</div>
</div>
</blockquote>
<br>
<pre cols="72">--
============================================================
Ivan A. Uemlianin PhD
Llaisdy
Speech Technology Research and Development
<a href="mailto:ivan@llaisdy.com" target="_blank">ivan@llaisdy.com</a>
@llaisdy
<a href="http://llaisdy.wordpress.com" target="_blank">llaisdy.wordpress.com</a>
<a href="http://github.com/llaisdy" target="_blank">github.com/llaisdy</a>
<a href="http://www.linkedin.com/in/ivanuemlianin" target="_blank">www.linkedin.com/in/ivanuemlianin</a>
festina lente
============================================================ </pre>
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