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comp.lang.ruby

array trouble

Gijs Nijholt

10/19/2006 2:59:00 PM

Hi

I want to add a value to an arrays' values like this:

ret = ""
"abcd".to_a.each do |w|
ret += " "
end

this gives => "abcd" in IRB
but I expected it to give "a b c d "

why doesnt this work as such?
thanks

gijs

--
Posted via http://www.ruby-....
7 Answers

Robert Klemme

10/19/2006 3:02:00 PM

0

On 19.10.2006 16:59, Gijs Nijholt wrote:
> Hi
>
> I want to add a value to an arrays' values like this:
>
> ret = ""
> "abcd".to_a.each do |w|
> ret += " "
> end
>
> this gives => "abcd" in IRB
> but I expected it to give "a b c d "
>
> why doesnt this work as such?

First, String#to_a does not what you probably expect:
irb(main):001:0> "abcd".to_a
=> ["abcd"]

Here are workable solutions:

irb(main):002:0> "abcd".gsub(/./, '\\& ')
=> "a b c d "
irb(main):003:0> "abcd".split(//).map {|s| s + " "}.join
=> "a b c d "

Kind regards

robert

Peter Szinek

10/19/2006 3:08:00 PM

0

Gijs Nijholt wrote:
> Hi
>
> I want to add a value to an arrays' values like this:
>
> ret = ""
> "abcd".to_a.each do |w|
> ret += " "
> end
>
> this gives => "abcd" in IRB
> but I expected it to give "a b c d "
How about

"abcd".split('').join(' ')

Peter
http://www.rubyra...

Tom Armitage

10/19/2006 3:21:00 PM

0

Also:

"abcd".split("").map do |w|
w + " "
end.join

would give you the extra space at the end.

On 19/10/06, Gijs Nijholt <gijs.nijholt@gmail.com> wrote:
> Hi
>
> I want to add a value to an arrays' values like this:
>
> ret = ""
> "abcd".to_a.each do |w|
> ret += " "
> end
>
> this gives => "abcd" in IRB
> but I expected it to give "a b c d "
>
> why doesnt this work as such?
> thanks
>
> gijs
>
> --
> Posted via http://www.ruby-....
>
>

Louis J Scoras

10/19/2006 3:23:00 PM

0

This should work also:

'abcd'.scan(/./).join(' ')


--
Lou.

Peter Szinek

10/19/2006 3:30:00 PM

0

Louis J Scoras wrote:
> This should work also:
>
> 'abcd'.scan(/./).join(' ')
>
>
Yeah, but it has the same flaw as mine (as pointed out by Tom):
"a b c d " != "a b c d"

but

'abcd'.scan(/./).join(' ') + " "

resp

"abcd".split('').join(' ') + " "

should solve also this problem...

Peter
http://www.rubyra...

Rick DeNatale

10/20/2006 5:55:00 PM

0

On 10/19/06, Gijs Nijholt <gijs.nijholt@gmail.com> wrote:
> Hi
>
> I want to add a value to an arrays' values like this:
>
> ret = ""
> "abcd".to_a.each do |w|
> ret += " "
> end
>
> this gives => "abcd" in IRB
> but I expected it to give "a b c d "
>
> why doesnt this work as such?
> thanks

Others have already given y

ou ways to do what you want to do. But I don't think anyone answered
your question about why what you did doesn't work.

Let's pick it apart. First of all it doesn't really return "abcd" it
returns ["abcd"] which is a array with a single element:

irb(main):001:0> ret = " "
irb(main):002:0> "abcd".to_a.each do |w| ret += " "; end
=> ["abcd"]

So why is this?

First of all, the value of Array#each is the array itself:

irb(main):003:0> [1, 2].each {|el| puts el }
1
2
=> [1, 2]

And, as Robert pointed out, "abcd".to_a doesn't do what you expect, it
returns an array of lines in the string, and there's only one line in
"abcd" so:

irb(main):004:0> "abcd".to_a
=> ["abcd"]

Now your code looks like it's trying to accumulate your result in ret,
lets' run it again, but we'll postpone the problem with String.to_a by
breaking up the array into characters, "by hand."

irb(main):005:0* ret = " "
irb(main):006:0> ["a", "b", "c", "d"].each { |w| ret += " " }
=> ["a", "b", "c", "d"]
irb(main):007:0> ret
=> " "

Oops, we weren't actually adding the elements, so ret just ended up as
a string with as many blanks as were characters. So let's fix that:

irb(main):008:0> ret = " "
rb(main):009:0> ["a", "b", "c", "d"].each { |w| ret += w + " " }
=> ["a", "b", "c", "d"]
irb(main):010:0> ret
=> " a b c d "

Okay, that looks better.

Now others have given one way to break up the string into an array of chars:

irb(main):011:0> "abcd".split(//)
=> ["a", "b", "c", "d"]

let's put this solution of the to_a problem with what we just did:

irb(main):012:0>ret = ''
rb(main):013:0> "abcd".split(//).each { |w| ret += w + " " }
=> ["a", "b", "c", "d"]
irb(main):014:0> ret
=> " a b c d "

So this works, as do the others. One more way to do this which is
related to the approach we've been taking is to use inject.

irb(main):018:0> "abcd".split(//).inject("") { |result, char| result
+= char + " " }
=> "a b c d "

This avoids having to use the auxiliary variable ret, since the result
of inject is the value accumulated in the first argument to it's block
argument.

--
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denh...

Gijs Nijholt

10/20/2006 6:40:00 PM

0

Thanks for all the replies, I really learned some important basics here.


Rick Denatale wrote:
> On 10/19/06, Gijs Nijholt <gijs.nijholt@gmail.com> wrote:
>> but I expected it to give "a b c d "
......
> --
> Rick DeNatale
>
> My blog on Ruby
> http://talklikeaduck.denh...


--
Posted via http://www.ruby-....