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Today's Topics:
1. comma delimited string (Bryce Verdier)
2. Re: comma delimited string (Daniel Fischer)
3. Re: Flying Dutchman sailing blind (Jeroen van Maanen)
4. Re: Flying Dutchman sailing blind (Daniel Fischer)
----------------------------------------------------------------------
Message: 1
Date: Thu, 14 Oct 2010 11:17:25 -0700
From: Bryce Verdier <[email protected]>
Subject: [Haskell-beginners] comma delimited string
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi All,
I have a file with a bunch of lines like such.
number,number,string,string,string,string
How can I split up the lines in Haskell so that each item in the line
becomes an element in a list? Or to put it differently, how do I split
up a comma delimited string?
Thanks in advance,
Bryce
------------------------------
Message: 2
Date: Thu, 14 Oct 2010 20:32:09 +0200
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-beginners] comma delimited string
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
On Thursday 14 October 2010 20:17:25, Bryce Verdier wrote:
> Hi All,
>
> I have a file with a bunch of lines like such.
> number,number,string,string,string,string
>
> How can I split up the lines in Haskell so that each item in the line
> becomes an element in a list? Or to put it differently, how do I split
> up a comma delimited string?
For example
http://hackage.haskell.org/packages/archive/split/0.1.2.1/doc/html/Data-
List-Split.html#v:splitWhen
http://hackage.haskell.org/packages/archive/split/0.1.2.1/doc/html/Data-
List-Split.html#v:splitOn
http://hackage.haskell.org/packages/archive/split/0.1.2.1/doc/html/Data-
List-Split.html#v:splitOneOf
do that for lists.
There's similar functionality for ByteStrings (bytestring, stringsearch)
and for Text (text).
>
> Thanks in advance,
>
> Bryce
------------------------------
Message: 3
Date: Fri, 15 Oct 2010 09:45:46 +0200
From: Jeroen van Maanen <[email protected]>
Subject: Re: [Haskell-beginners] Flying Dutchman sailing blind
To: Daniel Fischer <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
On 2010-10-13 15:53, Daniel Fischer wrote:
> On Wednesday 13 October 2010 14:52:58, Jeroen van Maanen wrote:
>> So in fact the culprit turned out to be the function updateRationals in
>> the module
>>
>>
>> http://lexau.svn.sourceforge.net/viewvc/lexau/branches/totem/src/LExAu/D
>> istribution/MDL.hs?view=markup
>>
>> It is still eating more time than the actual optimizer, so suggestions
>> for improvement are still welcome.
>
> First,
>
> approximateRational :: Double -> Rational
> [...]
>
> is exactly toRational, so there's no need for that function. Also, there's
> a much faster implementation of toRational (for Double and Float) underway,
> I think it will be in the first GHC 7 release due in a couple of weeks.
> Anyway, using toRational will let you profit from that with no additional
> effort when you get a compiler with that patch.
This was one of the first tricky bits that I converted from Java (in fact, it
was written in Clojure, a Lisp variant that runs on the Java virtual machine)
to Haskell. I was fighting with implicit type inference, and I didn't know then
how to fix the type of the value returned by the random number generator.
Thanks for pointing it out.
> Second, [Third ... Now updateRationals]
Thanks for taking me through this step-by-step. It helps me tremendously in
developing an intuition about what is going on in my program. It feels a bit
like when I started writing XSLT style-sheets. ;-)
Looking at the graphical presentation of heap usage[1] I guess that this solved
most of my heap problems. However the large amount allocated to TSO (I guess
that is Thread State Object) suggests to me that I still have an issue with
stack usage here.
Another thing that I noticed when I went over my algorithm again, is that the
list of weight/bound pairs is sorted according to the bound component on each
recursion step. This also happens when the produced data structure is used
later on in the program: I sort all pairs with a weight smaller than a certain
threshold by bound. Is there a some prepackaged data structure around that
would efficiently support this usage pattern?
Oh, and I Googled for "Haskell BLACKHOLE", but didn't find an explanation of
what it is. Is the amount of black holes on the heap of my program an
indication of some inefficiency that can be removed?
Cheers, Jeroen
[1] http://lexau.org/pub/lexau-heap.pdf
------------------------------
Message: 4
Date: Fri, 15 Oct 2010 11:32:33 +0200
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-beginners] Flying Dutchman sailing blind
To: Jeroen van Maanen <[email protected]>
Cc: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
On Friday 15 October 2010 09:45:46, Jeroen van Maanen wrote:
> On 2010-10-13 15:53, Daniel Fischer wrote:
> > On Wednesday 13 October 2010 14:52:58, Jeroen van Maanen wrote:
> >> So in fact the culprit turned out to be the function updateRationals
> >> in the module
> >>
> >>
> >> http://lexau.svn.sourceforge.net/viewvc/lexau/branches/totem/src/LExA
> >>u/D istribution/MDL.hs?view=markup
> >>
> >> It is still eating more time than the actual optimizer, so
> >> suggestions for improvement are still welcome.
> >
> > First,
> >
> > approximateRational :: Double -> Rational
> > [...]
> >
> > is exactly toRational, so there's no need for that function. Also,
> > there's a much faster implementation of toRational (for Double and
> > Float) underway, I think it will be in the first GHC 7 release due in
> > a couple of weeks. Anyway, using toRational will let you profit from
> > that with no additional effort when you get a compiler with that
> > patch.
>
> This was one of the first tricky bits that I converted from Java (in
> fact, it was written in Clojure, a Lisp variant that runs on the Java
> virtual machine) to Haskell. I was fighting with implicit type
> inference, and I didn't know then how to fix the type of the value
> returned by the random number generator. Thanks for pointing it out.
>
> > Second, [Third ... Now updateRationals]
>
> Thanks for taking me through this step-by-step. It helps me tremendously
> in developing an intuition about what is going on in my program. It
> feels a bit like when I started writing XSLT style-sheets. ;-)
>
> Looking at the graphical presentation of heap usage[1] I guess that this
> solved most of my heap problems.
According to that profile, your live heap starts out at between 3500 and
4000 kilobytes and decreases from then on. It may be less than optimal, but
a heap problem looks quite different.
You can get more info by doing profiling runs with -hc, -hb and so on.
> However the large amount allocated to
> TSO (I guess that is Thread State Object) suggests to me that I still
> have an issue with stack usage here.
You seem to fork/spark a lot of threads, so a lot of TSOs are generated.
>
> Another thing that I noticed when I went over my algorithm again, is
> that the list of weight/bound pairs is sorted according to the bound
> component on each recursion step. This also happens when the produced
> data structure is used later on in the program: I sort all pairs with a
> weight smaller than a certain threshold by bound. Is there a some
> prepackaged data structure around that would efficiently support this
> usage pattern?
>
> Oh, and I Googled for "Haskell BLACKHOLE", but didn't find an
> explanation of what it is. Is the amount of black holes on the heap of
> my program an indication of some inefficiency that can be removed?
I think section 8 of
http://www.haskell.org/~simonmar/papers/multicore-ghc.pdf
will be useful reading.
As a guess, it may help to set up some data single-threadedly before going
parallel.
>
> Cheers, Jeroen
>
> [1] http://lexau.org/pub/lexau-heap.pdf
------------------------------
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