# Contionnal sum **URL:** \ **Category:** Ruby\ **Created:** [May 15, 2008, 6:26pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724 "2008-05-15T18:26:22Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 6:26pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/1 "2008-05-15T18:26:22Z")
Hi, I am wondering if it is possible to create a conditionnal sum. For instance I would like to do something like this: @total\_amount = @orders.sum { |order| order.amount if order.paid == true } ---
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 6:44pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/2 "2008-05-15T18:44:15Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Fernando P. wrote: | Hi, | | I am wondering if it is possible to create a conditionnal sum. | | For instance I would like to do something like this: | | @total\_amount = @orders.sum { |order| order.amount if order.paid == true | } Should be. Something like this (untested, and unsafe, probably not even correct): def conditional\_sum order, condition ~ order.each do |o| ~ sum = sum + o unless o.paid? ~ end ~ return sum end I made the idea explicit, so that you should at least get the idea. * * * Phillip G. Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan) Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com) You! What PLANET is this! ~ – McCoy, “The City on the Edge of Forever”, stardate 3134.0 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (MingW32) Comment: Using GnuPG with Mozilla - [http://enigmail.mozdev.org](http://enigmail.mozdev.org) iEYEARECAAYFAkgsZ9UACgkQbtAgaoJTgL8L2gCeLZyAQcn6+o+4McD7qQLJlL1o qEUAn0JrnuPs7XVBNUYAEuCd6gUIsjBO =k8YY -----END PGP SIGNATURE----- ---
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 6:48pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/3 "2008-05-15T18:48:23Z")
On Thu, May 15, 2008 at 6:26 PM, Fernando P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I am wondering if it is possible to create a conditionnal sum. > > For instance I would like to do something like this: > > @total\_amount = @orders.sum { |order| order.amount if order.paid == true > } sum… is that Rails? If that’s the case you could filter them before: # untested @total\_sum = @orders.select(&:paid).sum(&:amount) Although AR has another SQL-based #sum that may be worth exploring if @orders are ARs. That being said, perhaps you weren’t aware of the fact that Enumerable#sum is defined by Active Support, but let me point out that those extensions are discussed in the very Rails mailing list. – fxn ---
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 7:36pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/4 "2008-05-15T19:36:06Z")
- Fernando P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) (18:26) schrieb: > Hi, > > I am wondering if it is possible to create a conditionnal sum. > > For instance I would like to do something like this: > > @total\_amount = @orders.sum { |order| order.amount if order.paid == true > } @total\_amount = @orders.inject(0) do | sum, order | order.paid ? sum + order.amount : sum end or @total\_amount = @orders.select { | o | o.paid }. sum BTW: Comparing a boolean value to true or false only shows you don’t understand booleans. And if that order class is yours: I’d rather call the accessor »paid?«. mfg, simon … l ---
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 7:40pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/5 "2008-05-15T19:40:47Z")
Xavier N. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > # untested > > @total\_sum = @orders.select(&:paid).sum(&:amount) > > Although AR has another SQL-based #sum that may be worth exploring if > @orders are ARs. > > That being said, perhaps you weren’t aware of the fact that > Enumerable#sum is defined by Active Support, but let me point out that > those extensions are discussed in the very Rails mailing list. Enumerable#sum is also in facets. The .select method is a good way, but you can use less memory by doing @orders.sum {|order| order.paid? order.amount : 0 } Facets’ #sum doesn’t skip nils, so the method you proposed won’t work. –Ken ---
**Author:** ![fipa](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/9e8a1a/32.png) [@fipa](https://www.ruby-forum.com/u/fipa)\ **Post date:** [May 15, 2008, 9:46pm UTC](https://www.ruby-forum.com/t/contionnal-sum/137724/6 "2008-05-15T21:46:47Z")
Thank you all for your messages. Yes it is a piece of code I am using in a Rails app. I thought it would fit better in this list rather than the Rails one, as the problem is not specific to Rails. > BTW: Comparing a boolean value to true or false only shows you don’t > understand booleans. Yeah I knew someone would nail me on this. I wanted to make my problem clear, so that’s why I specified this silly “== true”. In my real code, I don’t have it trust me. If I hadn’t put it, someone would have come up with “hey wtf is that order.paid thing!?” > The .select method is a good way, but you can use less memory by doing > > @orders.sum {|order| order.paid? order.amount : 0 } This is fantastic, I knew the solution was super simple. Day after day I love Ruby more and more. Best regards, and once again thank you very much for assisting me.