Array.new question

[Peter Szinek]

Hello,

1)
I would like to create an array of n empty arrays, i.e.

[ [], [], ... n-3 []'s, [] ]

So that the inner arrays are different objects.

Array.new(n,[]) does not help since the created arrays are not different
objects.

Is there an idiomatic way to accomplish this?

2) Is there an idiomatic way to do this (in a generic way, of course):

some_func(
[1,2,3]
[4,5,6]
[7,8,9] )

=> [ [1,4,7], [2,5,8], [3,6,9] ]

Thanks,
Peter
http://www.rubyrailways.com

 

[Alex Young]

Hello,

1)
I would like to create an array of n empty arrays, i.e.

[ [], [], ... n-3 []'s, [] ]

So that the inner arrays are different objects.

Array.new(n,[]) does not help since the created arrays are not different
objects.

Is there an idiomatic way to accomplish this?

a = (0..3).collect{[]} # => [[], [], [], []]
a[0][0] = 1
a # => [[1], [], [], []]

2) Is there an idiomatic way to do this (in a generic way, of course):

some_func(
[1,2,3]
[4,5,6]
[7,8,9] )

=> [ [1,4,7], [2,5,8], [3,6,9] ]

[1,2,3].zip([4,5,6],[7,8,9]) # => [[1,4,7], [2,5,8], [3,6,9]]

 

[Peter Szinek]

a = (0..3).collect{[]} # => [[], [], [], []]

a[0][0] = 1
a # => [[1], [], [], []]
Thx!

2) Is there an idiomatic way to do this (in a generic way, of course):

some_func(
[1,2,3]
[4,5,6]
[7,8,9] )

=> [ [1,4,7], [2,5,8], [3,6,9] ]

[1,2,3].zip([4,5,6],[7,8,9]) # => [[1,4,7], [2,5,8], [3,6,9]]

Sorry, I did not describe the scenario properly.
The thing is that I am iterating over an array (of arrays)
and I don't have the all the arrays at once (the inner arrays are
generated on the fly). Let me illustrate it:

input = [ [1,2,3], [4,5,6], [7,8,9] ]
result = []

input.each { |i| do_something_with(result, i) }

and the result should be

[ [1,4,7], [2,5,8], [3,6,9] ]

The question sounds: how is do_something_with implemented?
I have already implemented it but I don't think so it's a state-of-the
art solution

Thanks,
Peter
http://www.rubyrailways.com

 

[Alex Young]

a = (0..3).collect{[]} # => [[], [], [], []]
a[0][0] = 1
a # => [[1], [], [], []]
Thx!

2) Is there an idiomatic way to do this (in a generic way, of course):

some_func(
[1,2,3]
[4,5,6]
[7,8,9] )

=> [ [1,4,7], [2,5,8], [3,6,9] ]

[1,2,3].zip([4,5,6],[7,8,9]) # => [[1,4,7], [2,5,8], [3,6,9]]

Sorry, I did not describe the scenario properly.
The thing is that I am iterating over an array (of arrays)
and I don't have the all the arrays at once (the inner arrays are
generated on the fly). Let me illustrate it:

input = [ [1,2,3], [4,5,6], [7,8,9] ]
result = []

input.each { |i| do_something_with(result, i) }

and the result should be

[ [1,4,7], [2,5,8], [3,6,9] ]

The question sounds: how is do_something_with implemented?
I have already implemented it but I don't think so it's a state-of-the
art solution

Right... In that case, how about this:

input.each{|i| i.each_with_index{|x,j| (result[j] ||= []) << x}}

Not sure if it'll play the way you want with variable-length arrays, but
it puts the right contents in result.

 

[Ross Bamford]

Hello,

1)
I would like to create an array of n empty arrays, i.e.

[ [], [], ... n-3 []'s, [] ]

So that the inner arrays are different objects.

Array.new(n,[]) does not help since the created arrays are not different
objects.

Is there an idiomatic way to accomplish this?

a = (0..3).collect{[]} # => [[], [], [], []]
a[0][0] = 1
a # => [[1], [], [], []]

I think this will do the same thing, too:

a = Array.new(4) { [] }
# => [[], [], [], []]

a[0][0] = 1
# => 1

a
# => [[1], [], [], []]

 

[eden li]

input = [ [1,2,3], [4,5,6], [7,8,9] ]

result = []

input.each { |i| do_something_with(result, i) }

and the result should be

[ [1,4,7], [2,5,8], [3,6,9] ]

The question sounds: how is do_something_with implemented?
I have already implemented it but I don't think so it's a state-of-the
art solution

Not so state-of-the-art but succint:

def do_something_with_result(a, i)
i.each_with_index { |e, j|
a[j] ? a[j] << e : a << [e]
}
end

 

[Peter Szinek]

Alex,

Right... In that case, how about this:

input.each{|i| i.each_with_index{|x,j| (result[j] ||= []) << x}}

Not sure if it'll play the way you want with variable-length arrays, but
it puts the right contents in result.

Thx for the solution! Mine was totally the same (for the first time in
history since I am using Ruby as someone proposed on this list ;-)

Peter
http://www.rubyrailways.com

 

[Peter Szinek]

On 10/17/06, Peter Szinek <[email protected]> wrote:

You are simply brilliant

I am certainly very far from that... I was just happy that (still being
a noob) I have solved something on my own for the first time. What's
wrong with that?

Peter
http://www.rubyrailways.com

 

[Simon Kröger]

I am certainly very far from that... I was just happy that (still being
a noob) I have solved something on my own for the first time. What's
wrong with that?

Certainly nothing,

but i would like to add my own version:

input.each{|i| result << i}
result = result.transpose

cheers

Simon