## Feature #17608

closed### Compact and sum in one step

**Description**

Many use cases of `Array#sum`

are preceded with the `compact`

method or are followed by a block to ensure the value is addable.

```
a = [1, nil, 2, 3]
a.sum # !> TypeError
a.compact.sum # => 6
a.sum{_1 || 0} # => 6
```

I propose there should be a way to do that in one step. I request either of the following:

A. Change the current behaviour to skip `nil`

s.

```
a.sum # => 6
```

B. `Array#filter_sum`

method

```
a.filter_sum # => 6
```

C. An option for `Array#sum`

```
a.sum(compact: true) # => 6
```

#### Updated by Eregon (Benoit Daloze) over 2 years ago

`a.sum{_1 || 0}`

seems more than good enough.

I don't think we want composite methods unless there is a significant performance advantage and it's more expressive.

#### Updated by Hanmac (Hans Mackowiak) over 2 years ago

you can use that `nil.to_i`

returns 0

`a.sum(&:to_i) #=> 6`

#### Updated by sawa (Tsuyoshi Sawada) over 2 years ago

Hanmac (Hans Mackowiak) wrote in #note-6:

[Y]ou can use [the fact] that

`nil.to_i`

returns 0

`a.sum(&:to_i) #=> 6`

That won't work.

```
[1.2, nil, 3.6].sum{_1 || 0} # => 4.8
[1.2, nil, 3.6].sum(&:to_i) # => 4
```

#### Updated by marcandre (Marc-Andre Lafortune) over 2 years ago

Then use `sum(&:to_f)`

...

I agree, we should close this request.

#### Updated by Eregon (Benoit Daloze) over 2 years ago

**Status**changed from*Open*to*Rejected*

#### Updated by Eregon (Benoit Daloze) over 2 years ago

I closed it.

It seems clear there is no need for a new method or keyword argument, when `a.sum{_1 || 0}`

already works well, is clear and concise.

In general it's a good idea to think about what to do with missing data anyway, ignoring might not always be appropriate.

#### Updated by ko1 (Koichi Sasada) over 2 years ago

Many use cases of Array#sum are preceded with the compact

Can you count on your app or your observation?

```
ko1@aluminium:~$ gem-codesearch 'compact\.sum' | wc -l
75
```

not so many cases in gem-codesearch.

#### Updated by sawa (Tsuyoshi Sawada) over 2 years ago

ko1 (Koichi Sasada) wrote in #note-11:

Can you count on your app or your observation?

`ko1@aluminium:~$ gem-codesearch 'compact\.sum' | wc -l 75`

not so many cases in gem-codesearch.

I searched on my company's private repository (the `***`

in the following was replaced by the repository name):

https://github.com/search?q=org%3A**********+compact.sum&type=Code

and got 94 results. The search itself may match not only exactly `compact.sum`

but also strings like `compact_sum`

, so I checked through manually, and all of them were `compact.sum`

or a variant of it, like `&.compact&.sum`

.

When I switch to all results on GitHub:

https://github.com/search?l=Ruby&q=compact.sum&type=Code

it says 2,134, but this time, it includes strings like `compact_sum`

. I am not sure how many of them are genuine `compact.sum`

, but I believe there are many.

You presented the result on gems, but my guess is that `sum`

is a relatively newly introduced method, and so gems tend to avoid `sum`

in the first place to make them compatible with old Rubies, hence, gems are biased as data source for this purpose.

Search on Stack Overflow returns 21 questions that include `compact.sum`

.

https://stackoverflow.com/search?q=compact.sum

And please don't forget that, besides `compact.sum`

, code fragments like `sum{_1 || 0}`

are also relevant use cases.

#### Updated by naruse (Yui NARUSE) over 2 years ago

I think your code is actually `rel.pluck(:col).compact.sum`

.

It can be written as `rel.sum(:col)`

https://api.rubyonrails.org/v6.1.0/classes/ActiveRecord/Calculations.html#method-i-sum

#### Updated by mame (Yusuke Endoh) over 2 years ago

I think this is an endless argument. An idiom "`.compact.max`

" is 10x more frequent than "`.compact.sum`

" in GitHub search. If we introduce `Array#compact_max`

, then `#compact_min`

and `#compact_minmax`

should be also introduced. Next, why don't we need `#compact_max_by`

, `#compact_max_by`

, and `#compact_minmax_by`

? Maybe some people want `#compact_sort_by`

eventually.

We have never yet had combination methods `#sort_uniq`

and `#zip_map`

, which are clearly frequent idioms. You need to prove that `.compact.sum`

is really special, e.g., it is a critical performance bottleneck in multiple real-world applications, it is indisputably frequent (like `#filter_map`

), it is difficult to work around (like `#flat_map`

), etc.

#### Updated by Eregon (Benoit Daloze) about 2 years ago

FWIW, this was confirmed as rejected by matz:

https://github.com/ruby/dev-meeting-log/blob/master/DevelopersMeeting20210216Japan.md#feature-17608-compact-and-sum-in-one-step-sawa