Limit each do loop

Question

If I have the following,

<% @feed.sort_by{|t| - t.created_at.to_i}.each do |feed| %> 

<% end %>

How can limit it to only show the 10 most recent results

Solution 1

<% @feed.sort_by{|t| - t.created_at.to_i}.first(10).each do |feed| %>

However, it's probably best to push this down into the model like this

<% @feed.recent(10).each do |feed| %>

And, in fact, if @feed comes out of a database, I'd push it down even further: it doesn't make sense to load a ton of unsorted feed entries out of the DB, then sort them and then throw most of them away. Better let the DB do the sorting and filtering.

See @Peer Allan's answer for how to do it in ActiveRecord. In ARel (IOW: Rails 3) it would probably be even simpler, something like

Feed.all.order('created_at DESC').take(10)

Solution 2

Array#first(n)

[1,2,3,4,5].first(3)
=> [1,2,3]

Solution 3

I'd do it like this:

<% @array.limit(10).each do |a| %>

Solution 4

I agree with the others (Jörg in particular); but if you still want to know how to limit the loop itself, break can be useful.

@array.each_with_index do |feed, i|
  break if i == 10;
  # ...

Solution 5

The following code will return 10 recent records.

@feed = @feed.sort! { |a,b| b.created_at <=> a.created_at }.take(10)

Array Reference

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Comments

[Ed S.]

Why don't you just sort first and then slice the array to get the first 10?

[Victor]

If I wanna use @feed twice: one to show 10, another to show all, is it better for me to limit it in view with recent(10), then the next just normal for loop for @feed.

[Aleksander Pohl]

There are much better methods of limiting the number of displayed elements, than breaking the loop: first and [] operator work very well in such a scenario.

[Amadan]

I don't know about "better", but other answers are certainly nicer, which I specifically point out. "Better" is very situational; I might point out that the methods you propose make a new array, while mine doesn't. The point is, since the other answers already focused on limiting the collection itself, I answered just the literal question, adding another option: presupposing the loop over the whole collection, how to only run in 10 times max. It's not a solution I'd choose unless I was pressed for time, as it does make the code uglier.

[Aleksander Pohl]

Yes it's matter of style mostly. But if there is a direct concept expressing the intent of a programmer (like first, [] and order(...).take(10) especially) I personally find it more appealing to use it.

[mattd]

Awesome. This allows you to limit after doing the sort. In my case, I'm sorting on the highest number of polymorphic associations. I can't write a query for it (don't know how!). This works nicely.