<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body 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 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]) -><br>
lists:foldl(fun(Y, X) -><br>
<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) -><br>
case
<a class="moz-txt-link-freetext" href="maps:is_key(Key">maps:is_key(Key</a>, X) of<br>
false
-><br>
Value;<br>
true
-><br>
F(Key, Value, <a class="moz-txt-link-freetext" href="maps:get(Key">maps:get(Key</a>, X))<br>
end<br>
end,<br>
Y))<br>
end,<br>
Head,<br>
Tail).<br>
<br>
This has desired behaviour, and will probably still perform well.
Using lists:foldl is a brilliant idea.<br>
<br>
Best wishes<br>
<br>
Ivan<br>
<br>
<br>
<div class="moz-cite-prefix">On 26/08/2015 09:16, Alexander
Petrovsky wrote:<br>
</div>
<blockquote
cite="mid:CAH57y_RoFpPd8hc4191yf-FTDDUuni=W_i3bWnU3fuLH+cJ6uw@mail.gmail.com"
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 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) -> F(<a class="moz-txt-link-freetext" href="maps:get(Key">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">ivan@llaisdy.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">Dear All<br>
<br>
The maps module does not have a merge/3 like <a class="moz-txt-link-freetext" href="dict:merge/3">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 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 class="moz-txt-link-freetext" href="maps:fold(fun(K">maps:fold(fun(K</a>, V1, Acc) -><br>
case <a class="moz-txt-link-freetext" href="maps:is_key(K">maps:is_key(K</a>, Acc) of<br>
false -><br>
<a class="moz-txt-link-freetext" href="maps:put(K">maps:put(K</a>, V1, Acc);<br>
true -><br>
V2 = <a class="moz-txt-link-freetext" href="maps:get(K">maps:get(K</a>, Acc),<br>
<a class="moz-txt-link-freetext" href="maps:put(K">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"
href="mailto:ivan@llaisdy.com" target="_blank">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"
href="http://www.linkedin.com/in/ivanuemlianin"
rel="noreferrer" target="_blank">www.linkedin.com/in/ivanuemlianin</a><br>
<br>
festina lente<br>
============================================================<br>
<br>
_______________________________________________<br>
erlang-questions mailing list<br>
<a moz-do-not-send="true"
href="mailto:erlang-questions@erlang.org" target="_blank">erlang-questions@erlang.org</a><br>
<a moz-do-not-send="true"
href="http://erlang.org/mailman/listinfo/erlang-questions"
rel="noreferrer" target="_blank">http://erlang.org/mailman/listinfo/erlang-questions</a><br>
</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div class="gmail_signature">
<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 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>
</body>
</html>