Summing an array

Question

The code below passed tests on Ruby 1.8/1.9, but when I run these tests on Ruby 1.9.2, I'm getting no method errors for `Array#sum`. For example, ``` NoMethodError: undefined method `sum' for [3.2, 3.0, 1.5, 0.73, 0.47, 0.23]:Array ``` I came across `inject(:+)`, but when I tried to substitute it in where `sum` was, it created other problems. There's two methods where `sum` is used, `time_required` and `balance_queues`. In the second method, it was complicated to work it into the old code `q1.sum - q2.sum`. As much detail/explanation would be helpful. ``` class FairDistribution def initialize(jobs, num_of_queues) @queues = [ jobs.sort.reverse ] (num_of_queues - 1).times { @queues << [] } # Balance the queues until they are perfectly balanced while !balance_all_queues do; end end # Time required for all queues processing def time_required @queues.map { |q| q.sum }.max #SUM end # The actual distribution of jobs across the queues def distribution @queues end private # Runs through all qu…

Accepted Answer

`Enumerable#sum` is provided by ActiveSupport (part of Ruby on Rails). If you have the `active_support` gem installed, you can use `[].sum` by adding this to the top of your script:

```
require 'active_support/core_ext/enumerable'
```

Try using `.inject(0, :+)`. This will result in '0' for an empty array, and might have been the cause of your problems with `inject`.

Summing an array

Solution

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