Array.new question

Hello,

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?

  1. 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

Peter S. wrote:

objects.

Is there an idiomatic way to accomplish this?
a = (0…3).collect{[]} # => [[], [], [], []]
a[0][0] = 1
a # => [[1], [], [], []]

  1. 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]]

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

Thx!

  1. 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 :wink:

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

Peter S. wrote:

[4,5,6]
input = [ [1,2,3], [4,5,6], [7,8,9] ]
art solution :wink:
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.

On 10/17/06, Peter S. [email protected] wrote:

Hello,

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

[ [], [], … n-3 []'s, [] ]

Nicely answered

  1. 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] ]

I suppose you forgot the “,” if you forgot the enclosing “[”, “]” just
remove the splash operator (*) below:

some_func( *[0…n-1].map{|line| [nline+1…nline+n] } )

It is quit ugly maybe you should seek for less concentrated code though
:wink:
The parser is doing a great job here, I am really abusing it :frowning:

HTH
Robert

Thanks,

Peter
http://www.rubyrailways.com


The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.

  • George Bernhard Shaw

I have already implemented it but I don’t think so it’s a state-of-the
art solution :wink:

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

On Tue, 2006-10-17 at 18:08 +0900, Alex Y. wrote:

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], [], [], []]

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 :slight_smile: as someone proposed on this list :wink:

Peter
http://www.rubyrailways.com

On 10/17/06, Peter S. [email protected] wrote:

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

You are simply brilliant :wink:

Peter

http://www.rubyrailways.com


The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.

  • George Bernhard Shaw

Peter S. schrieb:

Robert D. wrote:

On 10/17/06, Peter S. [email protected] wrote:

You are simply brilliant :wink:

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

Robert D. wrote:

On 10/17/06, Peter S. [email protected] wrote:

You are simply brilliant :wink:

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

On 10/17/06, Peter S. [email protected] wrote:

Robert D. wrote:

On 10/17/06, Peter S. [email protected] wrote:

You are simply brilliant :wink:

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?

Did you see the smiley Peter? I meant that somebody coming up with the
same
thingy than me will be brilliant because we all think that we are
brilliant,
but only in the joke.
So there is definitely nothing wrong at all and it is quite impressive
for
someone new to ruby.
However it is quite a headache to maintain, I did not add any more
readable
forms, using e.g. #inject because I thaught that this will be perfectly
at
your fingertips.

Simon has added a version I think is most readable, it is probably a
very
good thing to use.

Here is an alternative using #inject - I do not like inject - but I am a
pro, I will not let getting feelings in my way :wink: <—N.B. Smiley

n.inject([]){
|a,k| a << [kn+1…(k+1)*n]
}

Furthermore that leaves a little challange for yourself, unless you
dislike
the magic dot notation.

Cheers
Robert

Peter
http://www.rubyrailways.com


The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all progress
depends on the unreasonable man.

  • George Bernhard Shaw

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