sorted-map-by issue?
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get their
values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
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Re: sorted-map-by issue?
Sorry, it's my mistake.
Because treep map use the comparator to compare keys, and if the comparator
returns 1 constantly,it can not find the item that equals the key.
So i can modified the example,and it works:
user= (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
2
user= (:b (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
1
2013/6/6 dennis zhuang killme2...@gmail.com
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get
their values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
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Re: sorted-map-by issue?
Your comparator #(if (= %1 %2) 0 1) may happen to give the correct answers
for your example sorted-maps, but it is also a bad comparator that will
fail for larger examples:
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
user= (:z (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
That is because if two items are not =, by returning 1 you are telling the
caller the first argument should come after the second argument. Thus if
at some time the comparator is called as (cmp :a :z), and later it is
called as (cmp :z :a), it returns the inconsistent results that :a should
come after :z, and later that :z should come after :a. No sorted tree can
hope to return correct results given such an inconsistent comparator.
More examples and discussion at the link below, if you are interested:
https://github.com/jafingerhut/thalia/blob/master/doc/other-topics/comparators.md
Andy
On Thu, Jun 6, 2013 at 4:19 AM, dennis zhuang killme2...@gmail.com wrote:
Sorry, it's my mistake.
Because treep map use the comparator to compare keys, and if the
comparator returns 1 constantly,it can not find the item that equals the
key.
So i can modified the example,and it works:
user= (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
2
user= (:b (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
1
2013/6/6 dennis zhuang killme2...@gmail.com
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get
their values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
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Re: sorted-map-by issue?
Thanks,you are right.I want to creat a map which keeps elements in
insertion order, but clojure doesn‘t have.
在 2013-6-6 下午10:02，Andy Fingerhut andy.finger...@gmail.com写道：
Your comparator #(if (= %1 %2) 0 1) may happen to give the correct answers
for your example sorted-maps, but it is also a bad comparator that will
fail for larger examples:
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
user= (:z (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
That is because if two items are not =, by returning 1 you are telling the
caller the first argument should come after the second argument. Thus if
at some time the comparator is called as (cmp :a :z), and later it is
called as (cmp :z :a), it returns the inconsistent results that :a should
come after :z, and later that :z should come after :a. No sorted tree can
hope to return correct results given such an inconsistent comparator.
More examples and discussion at the link below, if you are interested:
https://github.com/jafingerhut/thalia/blob/master/doc/other-topics/comparators.md
Andy
On Thu, Jun 6, 2013 at 4:19 AM, dennis zhuang killme2...@gmail.comwrote:
Sorry, it's my mistake.
Because treep map use the comparator to compare keys, and if the
comparator returns 1 constantly,it can not find the item that equals the
key.
So i can modified the example,and it works:
user= (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
2
user= (:b (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
1
2013/6/6 dennis zhuang killme2...@gmail.com
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get
their values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
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Re: sorted-map-by issue?
A few people, I believe primarily Alan Malloy and Anthony Grimes, have
created a Clojure library for what they call ordered sets and maps that do
exactly this. They are implemented not as you tried to do, but by
remembering a number for each element (for ordered sets) or key (for
ordered maps) that is the relative order that it was added in.
https://github.com/flatland/ordered
Andy
On Thu, Jun 6, 2013 at 7:56 AM, dennis zhuang killme2...@gmail.com wrote:
Thanks,you are right.I want to creat a map which keeps elements in
insertion order, but clojure doesn‘t have.
在 2013-6-6 下午10:02，Andy Fingerhut andy.finger...@gmail.com写道：
Your comparator #(if (= %1 %2) 0 1) may happen to give the correct answers
for your example sorted-maps, but it is also a bad comparator that will
fail for larger examples:
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
user= (:z (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m 13
:h 8))
nil
That is because if two items are not =, by returning 1 you are telling
the caller the first argument should come after the second argument.
Thus if at some time the comparator is called as (cmp :a :z), and later it
is called as (cmp :z :a), it returns the inconsistent results that :a
should come after :z, and later that :z should come after :a. No sorted
tree can hope to return correct results given such an inconsistent
comparator.
More examples and discussion at the link below, if you are interested:
https://github.com/jafingerhut/thalia/blob/master/doc/other-topics/comparators.md
Andy
On Thu, Jun 6, 2013 at 4:19 AM, dennis zhuang killme2...@gmail.comwrote:
Sorry, it's my mistake.
Because treep map use the comparator to compare keys, and if the
comparator returns 1 constantly,it can not find the item that equals the
key.
So i can modified the example,and it works:
user= (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
2
user= (:b (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
1
2013/6/6 dennis zhuang killme2...@gmail.com
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get
their values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
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Re: sorted-map-by issue?
The java core library also provides LinkedHashMap which preserves insertion
order, although this is a mutable bash-in-place data structure rather than
an immutable persistent data structure.
On Jun 6, 2013 4:06 PM, Andy Fingerhut andy.finger...@gmail.com wrote:
A few people, I believe primarily Alan Malloy and Anthony Grimes, have
created a Clojure library for what they call ordered sets and maps that do
exactly this. They are implemented not as you tried to do, but by
remembering a number for each element (for ordered sets) or key (for
ordered maps) that is the relative order that it was added in.
https://github.com/flatland/ordered
Andy
On Thu, Jun 6, 2013 at 7:56 AM, dennis zhuang killme2...@gmail.comwrote:
Thanks,you are right.I want to creat a map which keeps elements in
insertion order, but clojure doesn‘t have.
在 2013-6-6 下午10:02，Andy Fingerhut andy.finger...@gmail.com写道：
Your comparator #(if (= %1 %2) 0 1) may happen to give the correct
answers for your example sorted-maps, but it is also a bad comparator that
will fail for larger examples:
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m
13 :h 8))
nil
user= (:z (sorted-map-by #(if (= %1 %2) 0 1) :z -26 :b 1 :a 2 :c 3 :m
13 :h 8))
nil
That is because if two items are not =, by returning 1 you are telling
the caller the first argument should come after the second argument.
Thus if at some time the comparator is called as (cmp :a :z), and later it
is called as (cmp :z :a), it returns the inconsistent results that :a
should come after :z, and later that :z should come after :a. No sorted
tree can hope to return correct results given such an inconsistent
comparator.
More examples and discussion at the link below, if you are interested:
https://github.com/jafingerhut/thalia/blob/master/doc/other-topics/comparators.md
Andy
On Thu, Jun 6, 2013 at 4:19 AM, dennis zhuang killme2...@gmail.comwrote:
Sorry, it's my mistake.
Because treep map use the comparator to compare keys, and if the
comparator returns 1 constantly,it can not find the item that equals the
key.
So i can modified the example,and it works:
user= (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
2
user= (:b (sorted-map-by #(if (= %1 %2) 0 1) :b 1 :a 2))
1
2013/6/6 dennis zhuang killme2...@gmail.com
user= (sorted-map-by (constantly 1) :b 1 :a 2)
{:b 1, :a 2}
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
user= (keys (sorted-map-by (constantly 1) :b 1 :a 2))
(:b :a)
user= (count (sorted-map-by (constantly 1) :b 1 :a 2))
2
user= (:a (sorted-map-by (constantly 1) :b 1 :a 2))
nil
It looks so strange.The result map has keys :a and :b,but i can't get
their values.
Why? I try to hack the code,but i can't find the reason.
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
庄晓丹
Email:killme2...@gmail.com xzhu...@avos.com
Site: http://fnil.net
Twitter: @killme2008
--
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