Hi,
I’ve got an array a= [1,2,3,4,5,6] and want to access each second
element:
b=[2,4,6]. How is this done in ruby?
I know, that I can use a for-loob and modulo operator, but I think there
is a “ruby way” of doing this.
Thanks.
tomas
On Mar 12, 2006, at 9:34 PM, Tomas F. wrote:
Thanks.
tomas–
Posted via http://www.ruby-forum.com/.
require ‘enumerator’
a = (1…10).to_a
p a.enum_for(:each_slice, 2).collect { |m| m[1] } # → [2, 4, 6, 8, 10]
– Daniel
I’ve got an array a= [1,2,3,4,5,6] and want to access each second
element:
b=[2,4,6]. How is this done in ruby?
This is ugly, but it works:
a = [1,2,3,4,5,6]
(1…a.length).step(2) { |i| puts a[i] }
-Harold
Daniel H. wrote:
is a “ruby way” of doing this.
p a.enum_for(:each_slice, 2).collect { |m| m[1] } # -> [2, 4, 6, 8, 10]– Daniel
enumerator is handy but it seems a bit like overkill for a task that can
be done with the builtin classes:
irb(main):009:0> ary = [1,2,3,4,5,6]
=> [1, 2, 3, 4, 5, 6]
irb(main):010:0> ary2 = []
=> []
irb(main):011:0> ary.each_with_index { |a, i| ary2 << a if i % 2 == 1 }
=> [1, 2, 3, 4, 5, 6]
irb(main):012:0> ary2
=> [2, 4, 6]
array.inject(false) do |alternate,element|
if alternate
# Your processing
end
!alternate
end
Daniel H. wrote:
is a “ruby way” of doing this.
p a.enum_for(:each_slice, 2).collect { |m| m[1] } # -> [2, 4, 6, 8, 10]– Daniel
f=1
[1,2,3,4,5,6].select{f=!f}.each{|x|p x}
Daniel H. wrote:
is a “ruby way” of doing this.
– Daniel
I might do it this way:
map , = (1…10).partition{|i| i%2==0}
map.each {|i| puts a[i]}
or this way
a.each_with_index {|a,i| if i%2 == 0; … ; end}
Depending on my needs and mood
On 12 mars 06, at 21:34, Tomas F. wrote:
I’ve got an array a= [1,2,3,4,5,6] and want to access each second
element:
b=[2,4,6]. How is this done in ruby?
irb(main):001:0> a = [1,2,3,4,5,6]
=> [1, 2, 3, 4, 5, 6]
irb(main):002:0> a.select {|e| a.index(e) % 2 == 1 }
=> [2, 4, 6]
On 3/12/06, Luc H. [email protected] wrote:
–
That’s a problem if there are duplicates in the array:
irb(main):012:0> a=[1,1,2,2,3,3,4,5]
=> [1, 1, 2, 2, 3, 3, 4, 5]
irb(main):013:0> a.select{|e| a.index(e) %2 == 1}
=> [5]
irb(main):014:0> s=true
=> true
irb(main):015:0> a.select{s=!s}
=> [1, 2, 3, 5]
irb(main):016:0>
-Adam
On Mon, 13 Mar 2006, Tomas F. wrote:
tomas
Fixnum#step is one of the easiest ways to do this:
harp:~ > cat a.rb
a = [1, 2, 3, 4, 5, 6]
1.step(a.size, 2){|i| p a[i]}
harp:~ > ruby a.rb
2
4
6
regards.
-a
On 13 mars 06, at 01:00, Adam S. wrote:
That’s a problem if there are duplicates in the array:
Yep, good catch.
Tomas F. wrote:
tomas
I’ve always been intrigued by creating a generalized enumeration system.
Have
you guys seen this: http://www.rubyweeklynews.org/20050710 : accessing
index
inside map. For example:
(1…10).collect.with_index { |v, i| v * i }
I think that is sweet! I wonder if it can be generalized enough to do
this:
file.collect.each_byte.with_index { |b, i| b + 1 }
Mike
[email protected] wrote:
returned (array vs. enumerator). It’s almost as if the call to
collect wasn’t a “real” call to collect, but rather a kind of
place-holder for a collect operation. I’m not sure.
Ok, what if you rearrange the order of the calls:
file.each_byte.with_index.collect { |b, i| b + 1 }
That’s more left-to-right object-oriented sounding. Come to think of it
I like
this better because now collect is at the end, and that is the the final
intent
(with the block being next to it).
Mike
Hi –
On Tue, 14 Mar 2006, Mike A. wrote:
tomas
I’ve always been intrigued by creating a generalized enumeration system.
Have you guys seen this: http://www.rubyweeklynews.org/20050710 : accessing
index inside map. For example:(1…10).collect.with_index { |v, i| v * i }
I think that is sweet! I wonder if it can be generalized enough to do this:
file.collect.each_byte.with_index { |b, i| b + 1 }
I’m not sure why, but to my eye this has always looked somewhat
obscure. I guess it’s something about having to read to the right,
even to the extent of not seeing a block, before I know what’s being
returned (array vs. enumerator). It’s almost as if the call to
collect wasn’t a “real” call to collect, but rather a kind of
place-holder for a collect operation. I’m not sure.
David
–
David A. Black ([email protected])
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
“Ruby for Rails” chapters now available
from Manning Early Access Program! Ruby for Rails
Hi –
On Tue, 14 Mar 2006, Mike A. wrote:
b=[2,4,6]. How is this done in ruby?
returned (array vs. enumerator). It’s almost as if the call to
collect wasn’t a “real” call to collect, but rather a kind of
place-holder for a collect operation. I’m not sure.Ok, what if you rearrange the order of the calls:
file.each_byte.with_index.collect { |b, i| b + 1 }
That’s more left-to-right object-oriented sounding. Come to think of it I
like this better because now collect is at the end, and that is the the final
intent (with the block being next to it).
There’s still something I don’t like about using method-chaining
syntax for this. It may just be a failure of imagination on my part.
David
–
David A. Black ([email protected])
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)
“Ruby for Rails” chapters now available
from Manning Early Access Program! Ruby for Rails