finding Hash subsets based on key value
ee
Is there a simple way of searching the keys of a Hash to find a subset.
I have a set of keys with two values indicating group and sub-group,
eg:
group_1_item_1
group_2_item_2
group_1_item_2
group_1_item_4
group_2_item_3
I'd like to divide them into groups, but without having to loop through
the entire collection and having to test each key
Regards
Erik
Nura...@aol.com
maybe it's not the most elegant solution, but I'd create copies of the
original hash
for the subgroups and use the delete_if method for hashes to throw out
everything
that does not belong to group number n..
Best regards,
Axel
Martin DeMello
You can't get away without testing each key under the hood (this is
intrinsically an O(n) problem), but this should make it syntactically
convenient at least:
hash.partition {|k,v| k =~ /group_1/ }.map {|i| Hash[*i.flatten]}
Enumerable#partition divides your collection into two parts, based on
whether the block returns true or false, so it doesn't scale to more
than two subsets, but for your example it should work nicely.
martin
Robert Klemme
> ee <erik...@gmail.com> wrote:
>> Hi
>>
>> Is there a simple way of searching the keys of a Hash to find a
>> subset. I have a set of keys with two values indicating group and
>> sub-group, eg:
>>
>> group_1_item_1
>> group_2_item_2
>> group_1_item_2
>> group_1_item_4
>> group_2_item_3
>>
>> I'd like to divide them into groups, but without having to loop
>> through the entire collection and having to test each key
>
> You can't get away without testing each key under the hood (this is
> intrinsically an O(n) problem),
Definitely!
> but this should make it syntactically
> convenient at least:
>
> hash.partition {|k,v| k =~ /group_1/ }.map {|i| Hash[*i.flatten]}
>
> Enumerable#partition divides your collection into two parts, based on
> whether the block returns true or false, so it doesn't scale to more
> than two subsets, but for your example it should work nicely.
IMHO we should have a general partitioning method (probably in Enumerable)
that does partitioning into several buckets and not just two. Something
like this maybe:
module Enumerable
def general_partition
parts = Hash.new {|h,k| h[k] = self.class.new}
each do |x|
parts[yield(x)] << x
end
parts
end
end
class Hash
def << (x) self[x[0]] = x[1] end
end
>> h={1=>1,2=>2,3=>3}
=> {1=>1, 2=>2, 3=>3}
>> h.general_partition {|k,v| k % 3}
=> {0=>{3=>3}, 1=>{1=>1}, 2=>{2=>2}}
Opinions?
Kind regards
robert
Martin DeMello
>
> IMHO we should have a general partitioning method (probably in Enumerable)
> that does partitioning into several buckets and not just two. Something
> like this maybe:
>
> module Enumerable
> def general_partition
I like it, but not the name. partition_by, perhaps.
martin
Robert Klemme
Yes, this is *much* better!
robert
James Edward Gray II
The Set class has this feature and I even like the name:
irb(main):001:0> require "set"
=> true
irb(main):002:0> langs = Set.new([:perl, :python, :ruby])
=> #<Set: {:perl, :python, :ruby}>
irb(main):003:0> langs.classify { |m| m.to_s[0, 1] }
=> {"p"=>#<Set: {:perl, :python}>, "r"=>#<Set: {:ruby}>}
James Edward Gray II
Martin DeMello
>
> The Set class has this feature and I even like the name:
>
> irb(main):001:0> require "set"
> => true
> irb(main):002:0> langs = Set.new([:perl, :python, :ruby])
> => #<Set: {:perl, :python, :ruby}>
> irb(main):003:0> langs.classify { |m| m.to_s[0, 1] }
> => {"p"=>#<Set: {:perl, :python}>, "r"=>#<Set: {:ruby}>}
That *is* nice - wonder if there'd be any issues with moving it into
Enumerable.
martin
mark
And of course, I need to write the flight control software in Ruby,
because it is my favourite language. Anyone know how to control a
digital camera from ruby (under linux...)
Or, failing that, how to talk to a gps receiver? I'll need to
communicate with muxes as well.
Thanks,
Mark
Pit Capitain
>>irb(main):002:0> langs = Set.new([:perl, :python, :ruby])
>>=> #<Set: {:perl, :python, :ruby}>
>>irb(main):003:0> langs.classify { |m| m.to_s[0, 1] }
>>=> {"p"=>#<Set: {:perl, :python}>, "r"=>#<Set: {:ruby}>}
>
> That *is* nice - wonder if there'd be any issues with moving it into
> Enumerable.
Note that Set#classify creates a set for each group, which might not
always be what you want. IMO, Enumerable#classify should create arrays
instead.
Regards,
Pit
Martin DeMello
>
> Note that Set#classify creates a set for each group, which might not
> always be what you want. IMO, Enumerable#classify should create arrays
> instead.
I like Robert Klemme's implementation, where each Enumerable creates
partitions of its own type, and calls << on them to populate them. OTOH
it adds an additional dependency to Enumerable (<< as well as each), but
maybe it could default to Array if << doesn't exist.
martin
Hal Fulton
> ....gonna launch a computerized weather balloon, of couse!
> And of course, I need to write the flight control software in Ruby,
> because it is my favourite language. Anyone know how to control a
> digital camera from ruby (under linux...)
>
> Or, failing that, how to talk to a gps receiver? I'll need to
> communicate with muxes as well.
I can't help you offhand, but I just wanted to say this is the
coolest thing I've heard of in a month or more.
Actually, as for controlling devices... you might look into the
home automation realm. There are some Linux-based solutions there,
probably including security cameras and such.
Hal
nobuyoshi nakada
At Tue, 14 Jun 2005 18:44:00 +0900,
mark wrote in [ruby-talk:145336]:
> Or, failing that, how to talk to a gps receiver? I'll need to
> communicate with muxes as well.
I often use gpstrans on Linux.
<http://sourceforge.net/projects/gpstrans/>
--
Nobu Nakada
Steven Jenkins
> mark wrote:
>
>> ....gonna launch a computerized weather balloon, of couse!
>> And of course, I need to write the flight control software in Ruby,
>> because it is my favourite language. Anyone know how to control a
>> digital camera from ruby (under linux...)
>>
>> Or, failing that, how to talk to a gps receiver? I'll need to
>> communicate with muxes as well.
>
>
> I can't help you offhand, but I just wanted to say this is the
> coolest thing I've heard of in a month or more.
Ham radio geeks have been at this for a while:
http://users.crosspaths.net/~wallio/HABLinks.html
Also check out APRS: http://web.usna.navy.mil/~bruninga/aprs.html
Steve (N6UNI)
mark
mark
across the idea on the net, when I was looking for something to do to
remember a friend of mine who died. He would have loved the idea.
I'll have a look at the automation stuff. I need to be able to read gps
data, and send it back out over a TNC to a 2meter ham radio, so I can
find the darn thing again. I also need to be able to record still
pictures from a digital camera and record a movie from a webcam... all
without resorting to xwindows if possible... as I plan to run under
linux booting into console mode... with no monitor.
Thanks for the kind words!
Mark
Oh ya, the start of a website is at http://www.retrobbs.org/balloon
-----Original Message-----
From: Hal Fulton [mailto:hal...@hypermetrics.com]
Sent: 15 June 2005 00:19
To: ruby-talk ML
Subject: Re: Crazy Balloon flight computer software...
mark
after googling for days, I can't find anyone in the UK who is doing
this. Maybe it is because the balloons end up in the Atlantic, very
much a worry for me.
If anyone has any info on this in the UK (I know this is getting off
topic) I'd sure appreciate it.
Thanks for the links!
Mark
Jeffrey Moss
want to look into the realm of microcontrollers for your project. There are
a lot of hobbyists who've written kernel modules and such for these GPS
modules.
Check this out: www.gumstix.org
I found that gumstix board a while back and decided to dive right in to the
realm of microcontrollers. Never tried compiling ruby on it, don't know how
easy that would be, maybe others have done it.
-Jeff
----- Original Message -----
From: "Hal Fulton" <hal...@hypermetrics.com>
To: "ruby-talk ML" <ruby...@ruby-lang.org>
Sent: Tuesday, June 14, 2005 5:18 PM
Subject: Re: Crazy Balloon flight computer software...