Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #30838 > unrolled thread

fmap(), "inverse" of Python map() function

Back to article view | Back to comp.lang.python

Contents

  fmap(), "inverse" of Python map() function vasudevram <vasudevram@gmail.com> - 2012-10-05 13:19 -0700
    Re: fmap(), "inverse" of Python map() function Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-05 15:31 -0600
    Re: fmap(), "inverse" of Python map() function Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-05 15:43 -0600
    Re: fmap(), "inverse" of Python map() function Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-10-05 18:52 -0400
    Re: fmap(), "inverse" of Python map() function Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-05 17:24 -0600
    Re: fmap(), "inverse" of Python map() function Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-10-05 19:30 -0400
      Re: fmap(), "inverse" of Python map() function vasudevram <vasudevram@gmail.com> - 2012-10-06 11:57 -0700
        Re: fmap(), "inverse" of Python map() function vasudevram <vasudevram@gmail.com> - 2012-10-06 15:07 -0700
        Re: fmap(), "inverse" of Python map() function vasudevram <vasudevram@gmail.com> - 2012-10-06 15:07 -0700
      Re: fmap(), "inverse" of Python map() function vasudevram <vasudevram@gmail.com> - 2012-10-06 11:57 -0700

#30838 — fmap(), "inverse" of Python map() function

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

- Vasudev Ram
www.dancingbison.com
jugad2.blogspot.com
twitter.com/vasudevram

[toc] | [next] | [standalone]

#30841

On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudevram@gmail.com> wrote:
>
> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function.html

Your fmap is a special case of reduce.

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

[toc] | [prev] | [next] | [standalone]

#30844

On Fri, Oct 5, 2012 at 3:31 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudevram@gmail.com> wrote:
>>
>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function.html
>
> 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

[toc] | [prev] | [next] | [standalone]

#30846

On Fri, Oct 5, 2012 at 5:31 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudevram@gmail.com> wrote:
>>
>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function.html
>
> 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

[toc] | [prev] | [next] | [standalone]

#30849

On Fri, Oct 5, 2012 at 4:52 PM, Devin Jeanpierre <jeanpierreda@gmail.com> wrote:
> On Fri, Oct 5, 2012 at 5:31 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
>> On Fri, Oct 5, 2012 at 2:19 PM, vasudevram <vasudevram@gmail.com> wrote:
>>>
>>> http://jugad2.blogspot.in/2012/10/fmap-inverse-of-python-map-function.html
>>
>> 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.

[toc] | [prev] | [next] | [standalone]

#30852

On Fri, Oct 5, 2012 at 7:24 PM, Ian Kelly <ian.g.kelly@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

[toc] | [prev] | [next] | [standalone]

#30896

On Saturday, October 6, 2012 5:01:40 AM UTC+5:30, Devin Jeanpierre wrote:
> On Fri, Oct 5, 2012 at 7:24 PM, Ian Kelly  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

Thanks to all who replied. Always good to learn something new.

- Vasudev

[toc] | [prev] | [next] | [standalone]

#30900

 
> 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

[toc] | [prev] | [next] | [standalone]

#30901

 
> 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

[toc] | [prev] | [next] | [standalone]

#30897

On Saturday, October 6, 2012 5:01:40 AM UTC+5:30, Devin Jeanpierre wrote:
> On Fri, Oct 5, 2012 at 7:24 PM, Ian Kelly  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

Thanks to all who replied. Always good to learn something new.

- Vasudev

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web