Asp Forum - Indexing system - ruby newbie

Adam Groves

3/1/2006 1:12:00 PM

Hi there,

I'm trying to write a class which converts a number into letters like
so:
0 => -
1 => A
10 => J
27 => AA

... ad infinitum. My class looks like this at the moment (please don't
laugh!)

def letter(number)
@index = number - 1
if @index == 0
return "-"
end
@index_string = ""
@index_array= []
while @index > 0 do
@remainder = @index%27
@index_array << @remainder
@index = @index/27
end
@index_array
@index_array.each do |i|
# I'm sure there's a better way to do this
@alphabet =
["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
@index_string << @alphabet[i-1]
end
return @index_string.reverse!
end

This works fine for the first round: 26 returns "Z". But 27 returns "AZ"
because @index_array is [0,1]. I'd appreciate any help (and tips on how
to write tighter code!)

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

18 Answers

Dave Burt

3/1/2006 1:31:00 PM

Adam Groves wrote:
> Hi there,
>
> I'm trying to write a class which converts a number into letters like
> so:
> 0 => -
> 1 => A
> 10 => J
> 27 => AA

Try this:

n = ""
while(n > 0)
s << ?A + n % 26 - 1
n /= 26
end
n << "-" if n.empty?
s.reverse

Also, your @alphabet is ("a".."z").to_a

Cheers,
Dave

Ross Bamford

3/1/2006 2:00:00 PM

On Wed, 2006-03-01 at 22:33 +0900, Dave Burt wrote:
> Adam Groves wrote:
> > Hi there,
> >
> > I'm trying to write a class which converts a number into letters like
> > so:
> > 0 => -
> > 1 => A
> > 10 => J
> > 27 => AA
>
> Try this:
>
> n = ""
> while(n > 0)
> s << ?A + n % 26 - 1
> n /= 26
> end
> n << "-" if n.empty?
> s.reverse
>
> Also, your @alphabet is ("a".."z").to_a

This isn't as good as Dave's (it's potentially *lots* slower for a
start) but, well, I'm just an #inject addict really...:

def letter(n)
(n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
end

letter(0)
# => "_"
letter(1)
# => "A"
letter(10)
# => "J"
letter(27)
# => "AA"
letter(397)
# => "OG"

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

Adam Groves

3/1/2006 2:09:00 PM

Hey thanks guys. I'm really enjoying learning ruby - especially because
the ruby community is so helpful.

Ross Bamford wrote:
> On Wed, 2006-03-01 at 22:33 +0900, Dave Burt wrote:
>> Try this:
>>
>> n = ""
>> while(n > 0)
>> s << ?A + n % 26 - 1
>> n /= 26
>> end
>> n << "-" if n.empty?
>> s.reverse
>>
>> Also, your @alphabet is ("a".."z").to_a
>
> This isn't as good as Dave's (it's potentially *lots* slower for a
> start) but, well, I'm just an #inject addict really...:
>
> def letter(n)
> (n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
> end
>
> letter(0)
> # => "_"
> letter(1)
> # => "A"
> letter(10)
> # => "J"
> letter(27)
> # => "AA"
> letter(397)
> # => "OG"

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

Adam Groves

3/1/2006 3:15:00 PM

Dear Ross,

it works a treat but I'm having a bit of trouble figuring out what's
going on.

(n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }

I get this:
if n<1
'_'
else

But I'm stuck here.

(1...n).inject("A") { |curr, i| curr.succ}

I still can't quite get my head around blocks beyond .each do |x|

Ross Bamford wrote:
> On Wed, 2006-03-01 at 22:33 +0900, Dave Burt wrote:
>> Try this:
>>
>> n = ""
>> while(n > 0)
>> s << ?A + n % 26 - 1
>> n /= 26
>> end
>> n << "-" if n.empty?
>> s.reverse
>>
>> Also, your @alphabet is ("a".."z").to_a
>
> This isn't as good as Dave's (it's potentially *lots* slower for a
> start) but, well, I'm just an #inject addict really...:
>
> def letter(n)
> (n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
> end
>
> letter(0)
> # => "_"
> letter(1)
> # => "A"
> letter(10)
> # => "J"
> letter(27)
> # => "AA"
> letter(397)
> # => "OG"

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

Edward Faulkner

3/1/2006 3:50:00 PM

On Thu, Mar 02, 2006 at 12:14:47AM +0900, Adam Groves wrote:
> But I'm stuck here.
>
> (1...n).inject("A") { |curr, i| curr.succ}
>
> I still can't quite get my head around blocks beyond .each do |x|

#inject is one of the basic tools of functional programming. That's
why it seems hard. It's a very different way of thinking. And also
very powerful.

That said, I think this case is a completely gratuitious use of
inject. The tipoff is that the argument "i" is completely ignored.

I like this much better:

def letter(n)
return '_' if n==0
n==1 ? "A" : letter(n-1).succ
end

regards,
Ed

Ross Bamford

3/1/2006 4:28:00 PM

On Thu, 2006-03-02 at 00:50 +0900, Edward Faulkner wrote:
> On Thu, Mar 02, 2006 at 12:14:47AM +0900, Adam Groves wrote:
> > But I'm stuck here.
> >
> > (1...n).inject("A") { |curr, i| curr.succ}
> >
> > I still can't quite get my head around blocks beyond .each do |x|
>
> #inject is one of the basic tools of functional programming. That's
> why it seems hard. It's a very different way of thinking. And also
> very powerful.
>
> That said, I think this case is a completely gratuitious use of
> inject. The tipoff is that the argument "i" is completely ignored.
>

Well, sorry, I didn't realise we had to use them all. I like to use it
where I want to give back something new from a block, but don't want:

a = []
something.each { |e| a << e end }
a

In this case it was just a snazzier alternative to doing the (n-1).times
and so on...

Did I say I'm an #inject *addict* ?

> I like this much better:
>
> def letter(n)
> return '_' if n==0
> n==1 ? "A" : letter(n-1).succ
> end
>

Well, to each his own, but (maybe this is a bit pathological,
though...):

def letter(n)
(1...n).inject("A") { |curr, i| curr.succ}
end

def letter2(n)
return '_' if n==0
n==1 ? "A" : letter2(n-1).succ
end

p letter(327021)
# => "ROSS"

p letter2(327021)
# => -:3:in `letter2': stack level too deep (SystemStackError)
from -:3:in `letter2'
from -:11

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

Ross Bamford

3/1/2006 4:37:00 PM

On Thu, 2006-03-02 at 00:14 +0900, Adam Groves wrote:
> Dear Ross,
>
> it works a treat but I'm having a bit of trouble figuring out what's
> going on.
>
> (n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
>
> I get this:
> if n<1
> '_'
> else
>
> But I'm stuck here.
>
> (1...n).inject("A") { |curr, i| curr.succ}
>
> I still can't quite get my head around blocks beyond .each do |x|

Inject is real easy, and very handy. It's just like 'each', except it
also allows the result of the previous iteration to be injected via the
first argument. For the first iteration, you provide the initial result.

For example:

a = [1,2,3,4,5]

a.inject(0) { |sum, i| sum + i }
# => 15

What happens is:

Block is called with sum = 0, i = 1
Block returns 1
Block is called with sum = 1, i = 2
Block returns 3
Block is called with sum = 3, i = 3
Block returns 6
Block is called with sum = 6, i = 4
Block returns 10
Block is called with sum = 10, i = 5
Block returns 15
No more elements, so inject returns 15.

In Ruby, inject allows you to omit the initial value, in which case the
first _two_ elements from the enumerable are passed to the first
iteration, with things proceeding as above from there, so I could have
written:

a.inject { |sum, i| sum + i }

And would have:

Block is called with sum = 1, i = 2
Block returns 3
Block is called with sum = 3, i = 3
Block returns 6
.
.
etc.

You can use inject for much more than just summing stuff up. Comes in
very handy for these cryptic one-lines (even if you have to 'misuse' it
a bit occasionally).

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

Pete

3/1/2006 4:43:00 PM

how about that?

(n < 1) ? "_" : (("A"[0] + n).chr)

n = 12
> M

> --- Ursprüngliche Nachricht ---
> Von: Ross Bamford <rossrt@roscopeco.co.uk>
> An: ruby-talk@ruby-lang.org (ruby-talk ML)
> Betreff: Re: Indexing system - ruby newbie
> Datum: Thu, 2 Mar 2006 01:37:06 +0900
>
> On Thu, 2006-03-02 at 00:14 +0900, Adam Groves wrote:
> > Dear Ross,
> >
> > it works a treat but I'm having a bit of trouble figuring out what's
> > going on.
> >
> > (n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
> >
> > I get this:
> > if n<1
> > '_'
> > else
> >
> > But I'm stuck here.
> >
> > (1...n).inject("A") { |curr, i| curr.succ}
> >
> > I still can't quite get my head around blocks beyond .each do |x|
>
> Inject is real easy, and very handy. It's just like 'each', except it
> also allows the result of the previous iteration to be injected via the
> first argument. For the first iteration, you provide the initial result

Pete

3/1/2006 4:46:00 PM

another one:

tab = ["_", ("A".."Z").to_a].flatten
puts tab[n]

> --- Ursprüngliche Nachricht ---
> Von: Ross Bamford <rossrt@roscopeco.co.uk>
> An: ruby-talk@ruby-lang.org (ruby-talk ML)
> Betreff: Re: Indexing system - ruby newbie
> Datum: Thu, 2 Mar 2006 01:37:06 +0900
>
> On Thu, 2006-03-02 at 00:14 +0900, Adam Groves wrote:
> > Dear Ross,
> >
> > it works a treat but I'm having a bit of trouble figuring out what's
> > going on.
> >
> > (n < 1) ? '_' : (1...n).inject("A") { |curr, i| curr.succ }
> >
> > I get this:
> > if n<1
> > '_'
> > else
> >
> > But I'm stuck here.
> >
> > (1...n).inject("A") { |curr, i| curr.succ}
> >
> > I still can't quite get my head around blocks beyond .each do |x|
>
> Inject is real easy, and very handy. It's just like 'each', except it
> also allows the result of the previous iteration to be injected via the
> first argument. For the first iteration, you provide the initial result

James Gray

3/1/2006 4:47:00 PM

On Mar 1, 2006, at 10:42 AM, Peter Ertl wrote:

> how about that?
>
> (n < 1) ? "_" : (("A"[0] + n).chr)

And we can shorten "A"[0] to ?A.

James Edward Gray II

comp.lang.ruby

Indexing system - ruby newbie

Adam Groves

Dave Burt

Ross Bamford

Adam Groves

Adam Groves

Edward Faulkner

Ross Bamford

Ross Bamford

Pete

Pete

James Gray

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