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fmap(), "inverse" of Python map() function
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vasudevram  
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 More options Oct 5 2012, 4:19 pm
Newsgroups: comp.lang.python
From: vasudevram <vasudev...@gmail.com>
Date: Fri, 5 Oct 2012 13:19:17 -0700 (PDT)
Local: Fri, Oct 5 2012 4:19 pm
Subject: fmap(), "inverse" of Python map() function
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Ian Kelly  
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 More options Oct 5 2012, 5:32 pm
Newsgroups: comp.lang.python
From: Ian Kelly <ian.g.ke...@gmail.com>
Date: Fri, 5 Oct 2012 15:31:35 -0600
Local: Fri, Oct 5 2012 5:31 pm
Subject: Re: fmap(), "inverse" of Python map() function
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On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudev...@gmail.com> wrote:

> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function...

Your fmap is a special case of reduce.

def fmap(functions, argument):
    return reduce(lambda result, func: func(result), functions, argument)


 
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Ian Kelly  
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 More options Oct 5 2012, 5:44 pm
Newsgroups: comp.lang.python
From: Ian Kelly <ian.g.ke...@gmail.com>
Date: Fri, 5 Oct 2012 15:43:31 -0600
Local: Fri, Oct 5 2012 5:43 pm
Subject: Re: fmap(), "inverse" of Python map() function
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On Fri, Oct 5, 2012 at 3:31 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudev...@gmail.com> wrote:

>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function...

> Your fmap is a special case of reduce.

> def fmap(functions, argument):
>     return reduce(lambda result, func: func(result), functions, argument)

In a more functional style, you could also use reduce to compose the
functions before applying them:

def compose(f, g):
    return lambda x: f(g(x))

def fmap(functions):
    return reduce(compose, reversed(functions))

# Allowing you to then do:
result = fmap(functions)(argument)

Cheers,
Ian


 
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Devin Jeanpierre  
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 More options Oct 5 2012, 6:53 pm
Newsgroups: comp.lang.python
From: Devin Jeanpierre <jeanpierr...@gmail.com>
Date: Fri, 5 Oct 2012 18:52:41 -0400
Local: Fri, Oct 5 2012 6:52 pm
Subject: Re: fmap(), "inverse" of Python map() function
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On Fri, Oct 5, 2012 at 5:31 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudev...@gmail.com> wrote:

>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function...

> Your fmap is a special case of reduce.

So is map.

def map(f, seq):
    return reduce(
        lambda rseq, newpre:
            rseq.append(f(newpre)) or rseq,
        seq,
        [])

"X is a special case of reduce" is basically the same as saying "X can
be implemented using a for loop". If it's meant as a complaint, it's a
poor one.

-- Devin


 
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Ian Kelly  
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 More options Oct 5 2012, 7:24 pm
Newsgroups: comp.lang.python
From: Ian Kelly <ian.g.ke...@gmail.com>
Date: Fri, 5 Oct 2012 17:24:14 -0600
Local: Fri, Oct 5 2012 7:24 pm
Subject: Re: fmap(), "inverse" of Python map() function
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On Fri, Oct 5, 2012 at 4:52 PM, Devin Jeanpierre <jeanpierr...@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 5:31 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote:
>> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudev...@gmail.com> wrote:

>>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function...

>> Your fmap is a special case of reduce.

> So is map.

I realize that.  My point is that the function *feels* more like a
variant of reduce than of map.

> If it's meant as a complaint, it's a poor one.

It's not.

 
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Devin Jeanpierre  
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 More options Oct 5 2012, 7:31 pm
Newsgroups: comp.lang.python
From: Devin Jeanpierre <jeanpierr...@gmail.com>
Date: Fri, 5 Oct 2012 19:30:57 -0400
Local: Fri, Oct 5 2012 7:30 pm
Subject: Re: fmap(), "inverse" of Python map() function
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On Fri, Oct 5, 2012 at 7:24 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote:
> I realize that.  My point is that the function *feels* more like a
> variant of reduce than of map.

>> If it's meant as a complaint, it's a poor one.

> It's not.

Fair enough all around. Sorry for misunderstanding.

-- Devin


 
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vasudevram  
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 More options Oct 6 2012, 2:57 pm
Newsgroups: comp.lang.python
From: vasudevram <vasudev...@gmail.com>
Date: Sat, 6 Oct 2012 11:57:58 -0700 (PDT)
Local: Sat, Oct 6 2012 2:57 pm
Subject: Re: fmap(), "inverse" of Python map() function
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Thanks to all who replied. Always good to learn something new.

- Vasudev


 
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vasudevram  
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 More options Oct 6 2012, 2:58 pm
Newsgroups: comp.lang.python
From: vasudevram <vasudev...@gmail.com>
Date: Sat, 6 Oct 2012 11:57:58 -0700 (PDT)
Local: Sat, Oct 6 2012 2:57 pm
Subject: Re: fmap(), "inverse" of Python map() function
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Thanks to all who replied. Always good to learn something new.

- Vasudev


 
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vasudevram  
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 More options Oct 6 2012, 6:07 pm
Newsgroups: comp.lang.python
From: vasudevram <vasudev...@gmail.com>
Date: Sat, 6 Oct 2012 15:07:00 -0700 (PDT)
Subject: Re: fmap(), "inverse" of Python map() function
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> Thanks to all who replied. Always good to learn something new.

P.S. A reader posted a good comment with Scala as well as Python code for a compose function (basically same functionality as fmap, or more - the compose once, run many times thing). It's the 4th comment on my blog post.

- Vasudev


 
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vasudevram  
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 More options Oct 6 2012, 6:07 pm
Newsgroups: comp.lang.python
From: vasudevram <vasudev...@gmail.com>
Date: Sat, 6 Oct 2012 15:07:00 -0700 (PDT)
Subject: Re: fmap(), "inverse" of Python map() function
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> Thanks to all who replied. Always good to learn something new.

P.S. A reader posted a good comment with Scala as well as Python code for a compose function (basically same functionality as fmap, or more - the compose once, run many times thing). It's the 4th comment on my blog post.

- Vasudev


 
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