Iterate over the first n elements of an array

Question

How can I iterate up to four objects of an array and not all? In the following code, it iterates over all objects. I need only the first four objects.

objects = Products.all(); arr=Array.new objects.each do |obj| arr << obj end p arr

Can it be done like objects=objects.slice(4), or is iteration the only way?

Edit:

I also need to print how many times the iteration happens, but my solution objects[0..3] (thanks to answers here) long.

i=0; arr=Array.new objects[0..3].each do |obj| arr << obj p i; i++; end

Are you just trying to grab the first four objects, or are you trying to iterate over the first four objects? You can use the take method to grab the first n objects if you just wanted to iterate over them: objects.take(4).each do... — Marc Talbot
– Marc Talbot, Commented Mar 20, 2012 at 2:59
Why not arr = Products.limit(4).to_a (but you probably don't even need the to_a)? Any time you find yourself saying Model.all you should think again (and then a third time). — mu is too short
– mu is too short, Commented Mar 20, 2012 at 3:00
@Yosef you want each_with_index ... also, ++ isn't a ruby operator — Kyle
– Kyle, Commented Mar 20, 2012 at 3:19

rainkinz · Accepted Answer · 2015-03-30 22:39:40Z

138

You can get first n elements by using

arr = objects.first(n)

http://ruby-doc.org/core-2.0.0/Array.html#method-i-first

edited Mar 30, 2015 at 22:39

rainkinz

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answered Apr 11, 2013 at 17:27

Kate

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1 Comment

Joshua Pinter Over a year ago

"Hey Ruby, you're slick AF."

Jack · Accepted Answer · 2012-03-20 02:42:17Z

61

I guess the rubyst way would go by

arr=Array.new objects[0..3].each do |obj| arr << obj end p arr;

so that with the [0..3] you create a subarray containing just first 4 elements from objects.

answered Mar 20, 2012 at 2:42

Jack

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2 Comments

mu is too short Over a year ago

Why iterate when just arr = objects[0..3] does the same thing?

Varun Garg Over a year ago

this is the ruby way, but I observed it was much slower when compared to iterating over integer index (0 to 3) and fetching element via it (objects[i[). possibly because of copy work

Mladen Jablanović · Accepted Answer · 2012-03-20 08:51:24Z

20

Enumerable#take returns first n elements from an Enumerable.

answered Mar 20, 2012 at 8:51

Mladen Jablanović

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1 Comment

Joshua Pinter Over a year ago

How does this differ from #first? Can #first only be used on an Array while #take can be used on any Enumerable?

Automatico · Accepted Answer · 2012-09-11 23:11:57Z

6

arr = objects[0..3]

Thats all. You dont need the rest

answered Sep 11, 2012 at 23:11

Automatico

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Comments

Kyle · Accepted Answer · 2012-05-31 04:38:09Z

2

You can splice the array like this objects[0,4]

objects[0,4] is saying: start at index 0 and give me 4 elements of the array.

arr = objects[0,4].inject([]) do |array, obj| array << obj end p arr

edited May 31, 2012 at 4:38

answered Mar 20, 2012 at 2:42

Kyle

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2 Comments

mu is too short Over a year ago

Why inject when just arr = objects[0,4] will do?

Kyle Over a year ago

I assumed the OP wanted to iterate over an array and do something other than just collect the elements.

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