Re: Booleans to string immutably? An easy one, probably...

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scala> val blue=true; val green=false; val red=true; val z =
List(("blue", blue), ("green", green), ("red", red)) filter (_._2) map
(_._1) mkString (", ")
blue: Boolean = true
green: Boolean = false
red: Boolean = true
z: String = blue, red

Ishaaq Chandy wrote:
> Yes but, given his example mkString on List(blue, red) will return
> "true, true" not "blue, red" as Charles indicates he wants.
>
> I'd say you'd be better off implementing your colour values as
> instances of a proper enumerated type (called Colour) and then work
> from that (assuming of course that you have a finite known
> enumeration of colours you want to work from).
>
> Ishaaq
>
> 2009/3/6 Christian Szegedy >
>
> I just want to say one word to you - just one word : mkString
>
>
> On 3/5/09, *Charles F. Munat* > wrote:
>
> I have a set of boolean vals. For the sake of this question, let's
> say they are colors:
>
> val blue = true val green = false val red = true
>
> I want to go through this set of vals and create a string with the
> colors in a comma-separated list, thus:
>
> val colors: String = "blue, red"
>
> I can think of lots of ways to do this mutably, but does anyone
> have a clever way to do it without resort to vars or ArrayBuffers?
>
> Thanks.
>
> Chas. Munat
>
>
>

- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

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Ishaaq Chandy wrote:
> Yes but, given his example mkString on List(blue, red) will return
> "true, true" not "blue, red" as Charles indicates he wants.

Yes, that's the problem with the previous replies. (Also, the mkString
part is easy. I got that -- though I should have mentioned it to avoid
confusion. The trick is to go from val names to strings.)

> I'd say you'd be better off implementing your colour values as instances
> of a proper enumerated type (called Colour) and then work from that
> (assuming of course that you have a finite known enumeration of colours
> you want to work from).

I'll have to think about this. It's a nice idea, but I'm not clear at
the moment how it solves the initial problem.

Thanks! (And thanks, David and Christian. I appreciate your replies.)

Chas.
>
> Ishaaq
>
> 2009/3/6 Christian Szegedy >
>
> I just want to say one word to you - just one word : mkString
>
>
> On 3/5/09, *Charles F. Munat* > wrote:
>
> I have a set of boolean vals. For the sake of this question,
> let's say they are colors:
>
> val blue = true
> val green = false
> val red = true
>
> I want to go through this set of vals and create a string with
> the colors in a comma-separated list, thus:
>
> val colors: String = "blue, red"
>
> I can think of lots of ways to do this mutably, but does anyone
> have a clever way to do it without resort to vars or ArrayBuffers?
>
> Thanks.
>
> Chas. Munat
>
>
>

This is very clever. I have to persist the colors, however, so I think
the other method suggested by Tony using vals will be easier. I like
this one, though.

Thanks,

Chas.

Alex Boisvert wrote:
> Here's another variation...
>
> object Flags {
> case class Flag(name: String, value: Boolean)
> def apply(l: Flag*) = l filter (_.value) map (_.name) mkString ", "
> }
>
> import Flags._
>
> val blue = Flag("blue", true)
> val green = Flag("green", false)
> val red = Flag("red", true)
>
> scala> Flags(blue, green, red)
> res0: String = blue, red
>

Perfect. Thanks.

Chas.

Tony Morris wrote:
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>
> scala> val blue=true; val green=false; val red=true; val z =
> List(("blue", blue), ("green", green), ("red", red)) filter (_._2) map
> (_._1) mkString (", ")
> blue: Boolean = true
> green: Boolean = false
> red: Boolean = true
> z: String = blue, red
>
> Ishaaq Chandy wrote:
>> Yes but, given his example mkString on List(blue, red) will return
>> "true, true" not "blue, red" as Charles indicates he wants.
>>
>> I'd say you'd be better off implementing your colour values as
>> instances of a proper enumerated type (called Colour) and then work
>> from that (assuming of course that you have a finite known
>> enumeration of colours you want to work from).
>>
>> Ishaaq
>>
>> 2009/3/6 Christian Szegedy > >
>>
>> I just want to say one word to you - just one word : mkString
>>
>>
>> On 3/5/09, *Charles F. Munat* > > wrote:
>>
>> I have a set of boolean vals. For the sake of this question, let's
>> say they are colors:
>>
>> val blue = true val green = false val red = true
>>
>> I want to go through this set of vals and create a string with the
>> colors in a comma-separated list, thus:
>>
>> val colors: String = "blue, red"
>>
>> I can think of lots of ways to do this mutably, but does anyone
>> have a clever way to do it without resort to vars or ArrayBuffers?
>>
>> Thanks.
>>
>> Chas. Munat
>>
>>
>>
>
> - --
> Tony Morris
> http://tmorris.net/
>
> S, K and I ought to be enough for anybody.
>
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On Fri, Mar 06, 2009 at 10:44:37AM -0800, Charles F. Munat wrote:
> Yes, that's the problem with the previous replies. (Also, the mkString
> part is easy. I got that -- though I should have mentioned it to avoid
> confusion. The trick is to go from val names to strings.)

In the not really serious suggestion category, there's also:

scala> val flags = List('blue -> true, 'red -> false, 'green -> true)
flags: List[(Symbol, Boolean)] = List(('blue,true), ('red,false), ('green,true))

scala> flags filter (_._2) map (_._1) mkString " "
res0: String = 'blue 'green