On 14.12.2007 16:39, Gregory Seidman wrote:
> On Sat, Dec 15, 2007 at 12:28:51AM +0900, Jari Williamsson wrote:
>> I'm going through lots of data where the result of the current is affected 
>> by the previous element. So what I would need is an
>> "each_with_previous {|current, prev|}"
>> ...to make it a bit more readable. Is there any built-in Ruby method that I 
>> might have overlooked, or should I build my own?
> 
> You can fake it pretty simply with inject. For example:
> 
>>> [ 1,2,3,4,5 ].inject { |prev,cur| puts "#{prev}, #{cur}"; cur }
> 1, 2
> 2, 3
> 3, 4
> 4, 5
> 
> Note that you do need the block to "return" (i.e. evaluate to) the current
> element so that it gets passed into the next iteration.

There is a subtlety: with your code there will be no previous for the 
first element.  Depending on what the OP needs you can as well do

irb(main):001:0> (1..5).inject(nil) {|prev,curr| p [prev,curr];curr}
[nil, 1]
[1, 2]
[2, 3]
[3, 4]
[4, 5]
=> 5

Jari, what kind of calculation do you do?

Cheers

	robert