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?
Best regards,
Jari Williamsson
Enumerable.each_cons(2) { |current, prev| ... }
Eivind.
On Dec 14, 2007 4:28 PM, Jari Williamsson <jari.williamsson@mailbox.swipnet.se> 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?
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.
Best regards,
Jari Williamsson
--Greg
On Sat, Dec 15, 2007 at 12:28:51AM +0900, Jari Williamsson wrote:
require 'enumerator'
[first, second, third].each_slice(2) do |prev,curr|
# do stuff
end
Except that you don't get a [nil,first] pair to start, you get [first,second].
You could also do something like:
[first, second, third].inject(nil) do |prev, curr|
# do stuff
curr
end
And curr is assigned to prev in the next iteration and the first iteration gets [nil,first]
-Rob
Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com
On Dec 14, 2007, at 10:28 AM, 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?Best regards,
Jari Williamsson
Take your pick:
irb(main):001:0> a = %w| a b c d e f g h |
=> ["a", "b", "c", "d", "e", "f", "g", "h"]
irb(main):002:0> require 'enumerator'
irb(main):003:0> a.each_cons(2){ |x,y| puts "#{x}-#{y}" }
a-b
b-c
c-d
d-e
e-f
f-g
g-h
irb(main):004:0> a.each_slice(2){ |x,y| puts "#{x}-#{y}" }
a-b
c-d
e-f
g-h
On Dec 14, 8:28 am, Jari Williamsson <jari.williams...@mailbox.swipnet.se> 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?
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
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, 5Note that you do need the block to "return" (i.e. evaluate to) the current
element so that it gets passed into the next iteration.
Robert Klemme wrote:
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]
=> 5Jari, what kind of calculation do you do?
I'll use different approaches for different situations. Starting inject with nil or first item will both become handy. Thanks!
The tasks are for analyzing musical data. The current note is most often dependent of previous context.
Best regards,
Jari Williamsson