# Map Or Collect Redux **URL:** \ **Category:** Ruby\ **Created:** [April 2, 2007, 3:13pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861 "2007-04-02T15:13:31Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 3:13pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/1 "2007-04-02T15:13:31Z")
Looking in the old archives of ruby-talk I found a thread in 2005 about using map or collect. As far as I know there is not difference between the two methods. I would like to know what everyone’s preference is? I like using collect. Stephen B. IV ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 3:17pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/2 "2007-04-02T15:17:31Z")
I think the aliases are there for a good syntactic reason. It seems to me that if you are just filtering out items which meet a certain criteria from one array to be put into a new one (say all elements which are even numbers) then you are collecting. If you’re actually performing a transformation on the elements then you are mapping one array space onto another. example arr = [1, 2, 3, 4, 5] arr.collect { |x| if x%2 == 0 then x end }.compact =\> [2, 4] # Seems like maybe it should be .filter instead of .collect arr = [1, 2, 3, 4, 5] arr.map { |x| x\*2 } =\> [2, 4, 6, 8, 10] ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 3:24pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/3 "2007-04-02T15:24:31Z")
On 02/04/07, Nicholas M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > arr = [1, 2, 3, 4, 5] > arr.collect { |x| if x%2 == 0 then x end }.compact > =\> [2, 4] > > # Seems like maybe it should be .filter instead of .collect This is more appropriate for Array#select (or reject). Personally I use map exclusively. Farrel ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 3:26pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/4 "2007-04-02T15:26:34Z")
On 02.04.2007 15:17, Nicholas M. wrote: > I think the aliases are there for a good syntactic reason. It seems > to me that if you are just filtering out items which meet a certain > criteria from one array to be put into a new one (say all elements > which are even numbers) then you are collecting. No, you are actually _selecting_. > If you’re actually > performing a transformation on the elements then you are mapping one > array space onto another. #map and #collect behave identical. They are just there to make people coming from different programming languages feel at home with Ruby faster. > example > > arr = [1, 2, 3, 4, 5] > arr.collect { |x| if x%2 == 0 then x end }.compact > =\> [2, 4] > > # Seems like maybe it should be .filter instead of .collect No, use #select - much more efficient and it does exactly what you are trying to accomplish above. Regards robert PS: for the record, I use #map as it is shorter to type and I am laz ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 4:02pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/5 "2007-04-02T16:02:37Z")
Enumerable#select is certainly what I was thinking of. Certainly having both collect and map would make it easier for developers coming from other languages to pick up ruby but often times I see code where these methods are both used. Ruby reads very nice and I prefer to use map just because it semantically makes more sense to me if I am performing some sort of transformation on the array elements. (Plus it is shorter to type : ) ). When I think of collecting elements I think of gathering or _selecting_ certain elements, collect just does not seem to imply that the elements will be changed in any way to me. ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 5:13pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/6 "2007-04-02T17:13:20Z")
I use map, but then I was a Mathematics major, which may have something to do with it … 😉 ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 4:44pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/7 "2007-04-02T16:44:42Z")
On 4/2/07, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Looking in the old archives of ruby-talk I found a thread in 2005 > about using map or collect. As far as I know there is not difference > between the two methods. I would like to know what everyone’s > preference is? I use map. It is shorter and for me it describes the operation better. Ryan ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 6:49pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/8 "2007-04-02T18:49:55Z")
What does Matz use? Stephen B. IV ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 11:07pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/9 "2007-04-02T23:07:48Z")
removed\_email\_address@domain.invalid wrote: > I would like to know what everyone’s preference is? > I like using collect. Mostly the non-smalltalk terms: map, find, find\_all, but reject. (map == mathematics background.) When I’m dealing with an ActiveRecord::AssociationProxy, find and find\_all are overridden by Rails, so I tend to use detect and select. I’m not sure I like that, though, vice just saying to\_a.find. Devin ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 11:34pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/10 "2007-04-02T23:34:51Z")
On 4/2/07, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Looking in the old archives of ruby-talk I found a thread in 2005 > about using map or collect. As far as I know there is not difference > between the two methods. I would like to know what everyone’s > preference is? I use map for the most part - the one place I occasionally use collect is when I’m mapping over a struct or class to pick out a few fields, e.g. books.collect {|b| [b.author, b.title]} If I were designing my own language, I’d have map be structure-preserving, and collect return an array, but that’s just my personal feeling. martin ---
**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\ **Post date:** [April 2, 2007, 7:15pm UTC](https://www.ruby-forum.com/t/map-or-collect-redux/90861/11 "2007-04-02T19:15:59Z")
On 4/2/07, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > What does Matz use? > > Stephen B. IV WWMD?