Hi,
I have pasted a simplified version of the problem you are trying to
understand. You cannot do a 'sum' on a collection that has a 'nil' as
one of its elements. If 'nil' happens to be the first element, you
will get the 'NoMethodError' , as the method '+' is called on it (as
shown in the error trace 'nil.+') . Also note that the elements of the
collection have to define the method '+' for sum to work.
'sum' works by using 'inject' which in turn takes the first element
(unless an initial value is provided) and calls + on it using the next
element in collection as the input, then takes the result and repeats
the process for all the rest of the elements
>> ar = [1,2,3]
=> [1, 2, 3]
>> ar.sum
=> 6
>> ar = [nil,2,3]
=> [nil, 2, 3]
>> ar.sum
NoMethodError: You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.+
from /Library/Ruby/Gems/1.8/gems/activesupport-2.3.3/lib/
active_support/core_ext/enumerable.rb:63:in `sum'
from (irb):16:in `inject'
...
>>
regards,
mvp
On Aug 26, 10:00 pm, "Ruby on Rails: Talk" <dazzaroo...@gmail.com>
wrote:
> I have the code which creates the following made up of an array of 3
> TreatLists each with a number of Treatlistitems (I've broken it up to
> make it easier to read).
>
> ?> @breakdown
> => [
> #<Treatlist:0x23b98ac @items=[
> #<Treatlistitem:0x2389ef4 @longname="Eye Brow Shape", @spend=17.0,
> @prodtreat="T", @numsold=2, @unitcost=10.0>]>,
>
> #<Treatlist:0x235df34
> @items=[#<Treatlistitem:0x235b16c @longname="Back Massage",
> @spend=10.0, @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x23597cc @longname="Hopi Ear Candles", @spend=10.0,
> @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x23582dc @longname="Back Massage (Essential Oils)",
> @spend=10.0, @prodtreat="T", @numsold=1, @unitcost=10.0>]>,
>
> #<Treatlist:0x2357a1c @items=[
> #<Treatlistitem:0x2351b30 @longname="Back Massage", @spend=10.0,
> @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x234f9fc @longname="Hopi Ear Candles", @spend=10.0,
> @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x234cf90 @longname="Eye Brow Shape", @spend=10.0,
> @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x2349db8 @longname="Full Leg Wax DSS", @spend=18.0,
> @prodtreat="T", @numsold=2, @unitcost=10.0>,
> #<Treatlistitem:0x23476bc @longname="Bridal Make Up", @spend=10.0,
> @prodtreat="T", @numsold=1, @unitcost=10.0>,
> #<Treatlistitem:0x2342fcc @longname="Collin Face Powder", @spend=10.0,
> @prodtreat="P", @numsold=1, @unitcost=10.0>]>]
>
> I'm trying to add together the 'spend' figures from each but only if
> prodtreat = T or P. When I try the following:
>
> >> @breakdown[1].items.sum{|item| item.spend if item.prodtreat == "T"}
>
> => 30.0
>
> it works!!!
>
> But when I try it with P ...
>
> >> @breakdown[1].items.sum{|item| item.spend if item.prodtreat == "P"}
>
> I get the following:
>
> NoMethodError: You have a nil object when you didn't expect it!
> You might have expected an instance of Array.
> The error occurred while evaluating nil.+
> from /Library/Ruby/Gems/1.8/gems/activesupport-2.2.2/lib/
> active_support/core_ext/enumerable.rb:63:in `sum'
> from (irb):65:in `inject'
> from /Library/Ruby/Gems/1.8/gems/activesupport-2.2.2/lib/
> active_support/core_ext/enumerable.rb:63:in `each'
> from /Library/Ruby/Gems/1.8/gems/activesupport-2.2.2/lib/
> active_support/core_ext/enumerable.rb:63:in `inject'
> from /Library/Ruby/Gems/1.8/gems/activesupport-2.2.2/lib/
> active_support/core_ext/enumerable.rb:63:in `sum'
> from /Library/Ruby/Gems/1.8/gems/activesupport-2.2.2/lib/
> active_support/core_ext/enumerable.rb:61:in `sum'
> from (irb):65
>
>
>
> I really have no idea why this is not working or not returning a zero
> value?! Any ideas please?
>
> Cheers
>
> Darren
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