Asp Forum - arbitrary indexes

Jason Nordwick

9/12/2006 4:05:00 PM

There has to be an easier way to do this.

If I have v=(1..99).to_a and I want to index the 20th to 30th elements, this is simply v[20,10]. But if I have a list of indexes i=[9, 11, 35, 47, 48, 55, 58, 63, 92, 96] that I want, I can't seem to find a simpler way than i.map{|x|v[x]} which seem like an aweful lot of syntax just for what is essentially "v[i]". Is there an easier way to do this?

-jason

(If your answer is "in Ruby it is easy to change the way basic primitive operate yourself and hose everybody else in the project", then please keep it to yourself... that answer is getting a little tiresome.)

10 Answers

e

9/12/2006 4:18:00 PM

Jason Nordwick wrote:
> There has to be an easier way to do this.
>
> If I have v=(1..99).to_a and I want to index the 20th to 30th elements,
> this is simply v[20,10]. But if I have a list of indexes i=[9, 11, 35,
> 47, 48, 55, 58, 63, 92, 96] that I want, I can't seem to find a simpler
> way than i.map{|x|v[x]} which seem like an aweful lot of syntax just for
> what is essentially "v[i]". Is there an easier way to do this?

array.values_at *i

> -jason
>
> (If your answer is "in Ruby it is easy to change the way basic primitive
> operate yourself and hose everybody else in the project", then please
> keep it to yourself... that answer is getting a little tiresome.)

My answer is to

A) look over the documentation (ri Array, ri Array#values_at)

B) --And I mean this in the kindest way--stop thinking about how
things should be comparing to other languages and just go with the flow.

--
Posted via http://www.ruby-....

Austin Ziegler

9/12/2006 4:18:00 PM

On 9/12/06, Jason Nordwick <jason@adapt.com> wrote:
> There has to be an easier way to do this.
>
> If I have v=(1..99).to_a and I want to index the 20th to 30th elements, this is simply v[20,10]. But if I have a list of indexes i=[9, 11, 35, 47, 48, 55, 58, 63, 92, 96] that I want, I can't seem to find a simpler way than i.map{|x|v[x]} which seem like an aweful lot of syntax just for what is essentially "v[i]". Is there an easier way to do this?

>> v.values_at(9, 11, 35, 47, 48, 55, 58, 63, 92, 96)
=> [10, 12, 36, 48, 49, 56, 59, 64, 93, 97]

-austin
--
Austin Ziegler * halostatue@gmail.com * http://www.halo...
* austin@halostatue.ca * http://www.halo...feed/
* austin@zieglers.ca

Kero van Gelder

9/12/2006 4:27:00 PM

> If I have v=(1..99).to_a and I want to index the 20th to 30th elements,
> this is simply v[20,10]. But if I have a list of indexes i=[9, 11, 35, 47,
> 48, 55, 58, 63, 92, 96] that I want, I can't seem to find a simpler way
> than i.map{|x|v[x]} which seem like an aweful lot of syntax just for what
> is essentially "v[i]". Is there an easier way to do this?

v.values_at(*i)

> (If your answer is "in Ruby it is easy to change the way basic primitive
> operate yourself and hose everybody else in the project", then please keep
> it to yourself... that answer is getting a little tiresome.)

So tempting not to answer at all... or to tell you to RTFM...

Gary Wright

9/13/2006 3:54:00 PM

On Sep 12, 2006, at 12:18 PM, Austin Ziegler wrote:

> On 9/12/06, Jason Nordwick <jason@adapt.com> wrote:
>> There has to be an easier way to do this.
>>
>> If I have v=(1..99).to_a and I want to index the 20th to 30th
>> elements, this is simply v[20,10]. But if I have a list of indexes
>> i=[9, 11, 35, 47, 48, 55, 58, 63, 92, 96] that I want, I can't
>> seem to find a simpler way than i.map{|x|v[x]} which seem like an
>> aweful lot of syntax just for what is essentially "v[i]". Is there
>> an easier way to do this?
>
>>> v.values_at(9, 11, 35, 47, 48, 55, 58, 63, 92, 96)
> => [10, 12, 36, 48, 49, 56, 59, 64, 93, 97]

Another nice thing about values_at is that it understands ranges:

a = Array.new(10) { |x| x*2 } #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

b = a.values_at(1,3,5..7) #=> [2, 6, 10, 12, 14]

Gary Wright

Rick DeNatale

9/14/2006 12:34:00 AM

On 9/13/06, gwtmp01@mac.com <gwtmp01@mac.com> wrote:

> Another nice thing about values_at is that it understands ranges:
>
> a = Array.new(10) { |x| x*2 } #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>
> b = a.values_at(1,3,5..7) #=> [2, 6, 10, 12, 14]

But not an array?!

irb(main):005:0> (0..10).to_a.values_at([2, 3, 4, 5])
TypeError: can't convert Array into Integer
from (irb):5:in `values_at'
from (irb):5
from :0

This seems a little inconsistent, it would seem better if it handled
any arguments which were enumerables containing integers.

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denh...

Hal E. Fulton

9/14/2006 12:40:00 AM

Rick DeNatale wrote:
> irb(main):005:0> (0..10).to_a.values_at([2, 3, 4, 5])
> TypeError: can't convert Array into Integer
> from (irb):5:in `values_at'
> from (irb):5
> from :0
>
> This seems a little inconsistent, it would seem better if it handled
> any arguments which were enumerables containing integers.
>

I see your point. But you can just use an asterisk
to expand it.

Hal

Jason Nordwick

9/14/2006 12:46:00 AM

What would seem most natural (and best) would be:

a[1,3,5,6,7] or more generally a[list] (a[*list] seems unnecessarily complex and would be inconsistent with a[x..y] that is allowed).

Is there a good reason this shouldn't be allowed? It would certainly simplify and shorten much of my code.

-j

Rick DeNatale wrote:
> On 9/13/06, gwtmp01@mac.com <gwtmp01@mac.com> wrote:
>
>> Another nice thing about values_at is that it understands ranges:
>>
>> a = Array.new(10) { |x| x*2 } #=> [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
>>
>> b = a.values_at(1,3,5..7) #=> [2, 6, 10, 12, 14]
>
> But not an array?!
>
> irb(main):005:0> (0..10).to_a.values_at([2, 3, 4, 5])
> TypeError: can't convert Array into Integer
> from (irb):5:in `values_at'
> from (irb):5
> from :0
>
> This seems a little inconsistent, it would seem better if it handled
> any arguments which were enumerables containing integers.
>

e

9/14/2006 1:01:00 AM

Jason Nordwick wrote:
> What would seem most natural (and best) would be:
>
> a[1,3,5,6,7] or more generally a[list] (a[*list] seems unnecessarily
> complex and would be inconsistent with a[x..y] that is allowed).
>
> Is there a good reason this shouldn't be allowed? It would certainly
> simplify and shorten much of my code.

It conflicts with the current implementation

[1, 2, 3, 4, 5][1, 3] # => [2, 3, 4]

On a tangent, if you find yourself doing a lot
of #values_at, you may want to consider possibly
changing your datastructure.

> -j

--
Posted via http://www.ruby-....

Jason Nordwick

9/14/2006 4:56:00 AM

Eero Saynatkari wrote:
> Jason Nordwick wrote:
>> What would seem most natural (and best) would be:
>>
>> a[1,3,5,6,7] or more generally a[list] (a[*list] seems unnecessarily
>> complex and would be inconsistent with a[x..y] that is allowed).
>>
>> Is there a good reason this shouldn't be allowed? It would certainly
>> simplify and shorten much of my code.
>
> It conflicts with the current implementation
>
> [1, 2, 3, 4, 5][1, 3] # => [2, 3, 4]
>

Oh course. That's (now) blindingly obvious. I don't think there is much I can do to prevent all the value_at calls. I can't really lay out my arrays differently to get better continuity, and I seem to be using value_at almost every line where there is a decent amount of computation. Overall, arbitrary indexing seems far more useful than range based indexing using the [start,len] notation. After all, there is already start../...stop notation. Too bad I guess.

-j

> On a tangent, if you find yourself doing a lot
> of #values_at, you may want to consider possibly
> changing your datastructure.
>
>> -j
>
>

Jason Nordwick

9/14/2006 5:02:00 AM

P.S., that is still no reason Enumerable[list] should not be allowed that I can see.

a=[0,11,22,33,44,55]
b=[1,3]

where a[b] would return [11,33]

even if this would look a little funny in its constant form:

a[[1,3]]

-j

Eero Saynatkari wrote:
> Jason Nordwick wrote:
>> What would seem most natural (and best) would be:
>>
>> a[1,3,5,6,7] or more generally a[list] (a[*list] seems unnecessarily
>> complex and would be inconsistent with a[x..y] that is allowed).
>>
>> Is there a good reason this shouldn't be allowed? It would certainly
>> simplify and shorten much of my code.
>
> It conflicts with the current implementation
>
> [1, 2, 3, 4, 5][1, 3] # => [2, 3, 4]
>
> On a tangent, if you find yourself doing a lot
> of #values_at, you may want to consider possibly
> changing your datastructure.
>
>> -j
>
>

comp.lang.ruby

arbitrary indexes

Jason Nordwick

e

Austin Ziegler

Kero van Gelder

Gary Wright

Rick DeNatale

Hal E. Fulton

Jason Nordwick

e

Jason Nordwick

Jason Nordwick

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