Rails - Aug 2005 - Creating a simple sum (or: I suck at blocks!)

I''ve been hacking on this for awhile and am not even getting close.  
Consider the following...

results = Sample.find(:all)
total_counter = results.each{|result| #Add together result.counter}

I just want to simply iterate through the list and sum the counter field 
for each row into an aggregation.  I could do it in a full for loop, but 
is there a nice one liner I''m missing?

Thanks,
Jeff

On Aug 23, 2005, at 10:14 AM, Jeff Casimir wrote:
> I''ve been hacking on this for awhile and am not even getting
close.
> Consider the following...
>
> results = Sample.find(:all)
> total_counter = results.each{|result| #Add together result.counter}
>
> I just want to simply iterate through the list and sum the counter 
> field for each row into an aggregation.  I could do it in a full for 
> loop, but is there a nice one liner I''m missing?
>
> Thanks,
> Jeff
You need to use inject for this:

total = results.inject(0) {|sum, result| sum + result.counter}

-Scott

On 8/23/05, Jeff Casimir <jeff-+RlNNtFrnNmT15sufhRIGw@public.gmane.org>
wrote:
> results = Sample.find(:all)
> total_counter = results.each{|result| #Add together result.counter}
> 
> I just want to simply iterate through the list and sum the counter field
> for each row into an aggregation.  I could do it in a full for loop, but
> is there a nice one liner I''m missing?
try this

   total_count = results.inject(0) { |sum, sample| sum + sample.counter }

Untested, but should work like this...

Sebastian

On 8/23/05, Jeff Casimir <jeff-+RlNNtFrnNmT15sufhRIGw@public.gmane.org>
wrote:
> I''ve been hacking on this for awhile and am not even getting
close.
> Consider the following...
> 
> results = Sample.find(:all)
> total_counter = results.each{|result| #Add together result.counter}
> 
> I just want to simply iterate through the list and sum the counter field
> for each row into an aggregation.  I could do it in a full for loop, but
> is there a nice one liner I''m missing?
> 
> Thanks,
> Jeff
results_sum = results.inject(0) { |sum, result| sum + result.counter }

#inject wass probably one of the hardest methods for me to learn.  

http://ruby-doc.org/core/classes/Enumerable.html#M001865

Just take a close look at all the array and enumerable methods.  


-- 
rick
http://techno-weenie.net

Jeff Casimir wrote:
> I''ve been hacking on this for awhile and am not even getting
close.
> Consider the following...
> 
> results = Sample.find(:all)
> total_counter = results.each{|result| #Add together result.counter}
> 
> I just want to simply iterate through the list and sum the counter field 
> for each row into an aggregation.  I could do it in a full for loop, but 
> is there a nice one liner I''m missing?
> 
> Thanks,
> Jeff
Not 100% sure about this but think it is what you want...

total_counter = results.collect { |result| total_counter += result.counter }

However, it seems it might be better to run a simple sql query for what 
you are trying to do..

"select sum(counter) from table_name"

Chris

Right:

irb(main):001:0> total = 0
=> 0
irb(main):002:0> results = [1,2,3,4,5,6]
=> [1, 2, 3, 4, 5, 6]
irb(main):003:0> total = results.inject(0) { |sum, res| sum + res }
=> 21


Wrong:

irb(main):001:0> total = 0
=> 0
irb(main):002:0> results = [1,2,3,4,5,6]
=> [1, 2, 3, 4, 5, 6]
irb(main):003:0> total = results.collect { | res | total += res }
=> [1, 3, 6, 10, 15, 21]

I would have guessed that both would exhibit the same behavior.  Color
me confused.

On 8/23/05, Chris Roos <chris-zoUjy1rb4AnQXOPxS62xeg@public.gmane.org>
wrote:
> Jeff Casimir wrote:
> > I''ve been hacking on this for awhile and am not even getting
close.
> > Consider the following...
> >
> > results = Sample.find(:all)
> > total_counter = results.each{|result| #Add together result.counter}
> >
> > I just want to simply iterate through the list and sum the counter
field
> > for each row into an aggregation.  I could do it in a full for loop,
but
> > is there a nice one liner I''m missing?
> >
> > Thanks,
> > Jeff
> 
> Not 100% sure about this but think it is what you want...
> 
> total_counter = results.collect { |result| total_counter += result.counter
}
> 
> However, it seems it might be better to run a simple sql query for what
> you are trying to do..
> 
> "select sum(counter) from table_name"
> 
> Chris
> 
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
> 

-- 
Brock Weaver
[OBC]Technique

Jeff Casimir wrote:
> I''ve been hacking on this for awhile and am not even getting
close.
> Consider the following...
> 
> results = Sample.find(:all)
> total_counter = results.each{|result| #Add together result.counter}
> 
> I just want to simply iterate through the list and sum the counter field 
> for each row into an aggregation.  I could do it in a full for loop, but 
> is there a nice one liner I''m missing?
> 
> Thanks,
> Jeff
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
> 
> 
Sorry, my recent post was incorrect.  You can still do either of these 
but I''d suggest Rick''s solution is ''better''.

a = [1, 2, 3, 4, 5]
b = 0; a.each { |val| b+=val }
OR
b = 0; a.collect { |val| b+=val }

Sorry for the incorrect advice initially.

Chris

On Aug 23, 2005, at 10:28 AM, Rick Olson wrote:
>>
>
> results_sum = results.inject(0) { |sum, result| sum + result.counter }
>
> #inject wass probably one of the hardest methods for me to learn.
>
> http://ruby-doc.org/core/classes/Enumerable.html#M001865
>
> Just take a close look at all the array and enumerable methods.
>
>
> -- 
> rick
> http://techno-weenie.net
>
Yeah, I often wish ruby had something like this (quick, off the top of 
my head hack):

module Enumerable
   def sum(&block)
     if block_given?
       self.inject(0) { |s, x| s + yield(x) }
     else
       self.inject(0) { |s, x| s + x }
     end
   end
end

puts [x, y, z].sum { |i| i.val }
puts [3, 6, 9].sum

If you really want to grok some of this stuff I recommend learning a 
functional
programming language.  Haskell is pretty sweet and easy to pick up.

-Scott

On Aug 23, 2005, at 10:29 AM, Chris Roos wrote:
> Jeff Casimir wrote:
>> I''ve been hacking on this for awhile and am not even getting
close.
>> Consider the following...
>> results = Sample.find(:all)
>> total_counter = results.each{|result| #Add together result.counter}
>> I just want to simply iterate through the list and sum the counter 
>> field for each row into an aggregation.  I could do it in a full for 
>> loop, but is there a nice one liner I''m missing?
>> Thanks,
>> Jeff
>
> Not 100% sure about this but think it is what you want...
>
> total_counter = results.collect { |result| total_counter += 
> result.counter }
>
Nope, #collect (aka #map) takes a collection and applies a block to 
each item and returns a collection
of the results of those applications, so you can''t get a single value 
out of it (without perverting
the concept entirely).

-Scott

> Wrong:
> 
> irb(main):001:0> total = 0
> => 0
> irb(main):002:0> results = [1,2,3,4,5,6]
> => [1, 2, 3, 4, 5, 6]
> irb(main):003:0> total = results.collect { | res | total += res }
> => [1, 3, 6, 10, 15, 21]
total = results.collect { | res | total += res }.last
=> 21

Wow fast moving thread.  I had an explanation but Scott beat me to it.
 And my above solution possibly qualifies as "perverting the concept."


-- 
rick
http://techno-weenie.net

On Aug 23, 2005, at 11:12 AM, Rick Olson wrote:
>> Wrong:
>>
>> irb(main):001:0> total = 0
>> => 0
>> irb(main):002:0> results = [1,2,3,4,5,6]
>> => [1, 2, 3, 4, 5, 6]
>> irb(main):003:0> total = results.collect { | res | total += res }
>> => [1, 3, 6, 10, 15, 21]
>
> total = results.collect { | res | total += res }.last
> => 21
>
> Wow fast moving thread.  I had an explanation but Scott beat me to it.
>  And my above solution possibly qualifies as "perverting the
concept."
>
>
> -- 
> rick
> http://techno-weenie.net
I give it a rating of XXX.  ;)

-Scott