From: Joel VanderWerf <vjoel@...>
Date: 2004-04-19T06:36:56+09:00
Subject: Re: How do I insert into an array?

Sam Roberts wrote:
> I want to add an item just before the end:
> 
> rb(main):003:0> a = [1,2,3]
> [1, 2, 3]
> irb(main):004:0> last=a.pop; a.push "second last"; a.push last
> [1, 2, "second last", 3]
> 
> 
> Is there a better way than this "pop,push,push" thing? I looked for an 
> Array.insert, but can't find anything like it.

Here's a way:

irb(main):001:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):002:0> a[-1,0] = "second last"
=> "second last"
irb(main):003:0> a
=> [1, 2, "second last", 3]

The -1 in a[-1,0] is obtained by counting backwards from the end of the 
array. The 0 is the size of the "selection" you want to "replace", so 0 
just means insert.

Another way is to use ranges:

irb(main):009:0> a = [1,2,3]
=> [1, 2, 3]
irb(main):010:0> a[2...2] = "second last"
=> "second last"
irb(main):011:0> a
=> [1, 2, "second last", 3]

Use the ... form instead of the .. form, or else a[2] will be replaced.