Some small suggestions to Array

I’m a new user of ruby from China. I love it very much. And I believe
it will become better and better in future. During the study of ruby
these days, I have some small suggestions to ruby.

The suggestions are about the array object, I think we may provide a
much much more flexible way to refer the elements from an array.
Suppose we have an array object [1,2,3,4,5], named “a”.
1.Now we have: a[from, len], The first parameter means the result will
start with a[from], and length is len. Then what about a[2,-3]? I think
a negative second parameter should means an reversed array, that is,
a[2,-3] shoule be [3,2,1].
Additionally, we may introduce a more flexible way to express the
“end with”. maybe like this: a[…2, 3] (means end with a[2], length is
3, normal direction). here “…2” means end with a[2], and obviously we
should let “2…” means “start with”.
Some examples:
a[2…, 3] == a[2,3] -> [3,4,5]
a[2…, -3] == a[2,-3] -> [3,2,1]
a[…2, 3] -> [1,2,3]
a[…2, 3] -> [5,4,3]
2.Now we have: a[2…3] and a[2…3] to discribe a closed interval and a
semi-open interval. I think we should provide an easy way to discrible
any kinds of interval, may be like this:
2…4 means 2,3,4
[2…4) means 2,3
(2…4] means 3,4
(2…4) means 3
the way above may be not beautiful enough, but the function is
required i guess.
Moreover, I guess a[3…1] should means [4,3,2]. it is just the
semantic of “from…to”
3.Some much more ideas:
a[i if odd?(i)] should be [2,4]
a[[1,3,3,4]] should be [2,4,4,5]
a[[1,3…4]] should be [2,4,5]
a[:]{|a[i]|, odd?(a[i])} should be [1,3,5], the block works as a
filter of the result.
And what about the combination of all above?
(Some ideas come from the grammar of matlab. Its array’s interface
is great.)

On Jan 25, 2007, at 16:40, 王谦 wrote:

I’m a new user of ruby from China. I love it very much. And I believe
it will become better and better in future. During the study of ruby
these days, I have some small suggestions to ruby.

您好!我很喜欢介绍您!
I second your open ranges (a[2…] gives a subarray starting from the
element with index 2 to the end) as i think they are quite intuitive.
But I’m also a newcomer to Ruby, and I wonder whether there already are
some beautiful ruby ways that give the desired results.

Your sincerely,
Damian/Three-eyed Fish

On 1/25/07, 王谦 [email protected] wrote:

I’m a new user of ruby from China. I love it very much. And I believe
it will become better and better in future. During the study of ruby
these days, I have some small suggestions to ruby.

Please, learn the language a bit more before you already give
suggestions, i know this sounds not very nice and we really appreciate
your suggestions, however, there are some quirks and standards in ruby
that you may not be aware of as you write this.
This should not mean that you have to be totally proficient in ruby
after a couple of days, it only means that, before you critizise
something you should have as much knowledge about it as possible.

The suggestions are about the array object, I think we may provide a
much much more flexible way to refer the elements from an array.
Suppose we have an array object [1,2,3,4,5], named “a”.
1.Now we have: a[from, len], The first parameter means the result will
start with a[from], and length is len. Then what about a[2,-3]? I think
a negative second parameter should means an reversed array, that is,
a[2,-3] shoule be [3,2,1].

negative indices count backwards, -1 is the equivalent of 0, but on
the other side of the array.
The way to do this right now:
a.reverse[2,3]

[3, 2, 1]

Additionally, we may introduce a more flexible way to express the
“end with”. maybe like this: a[…2, 3] (means end with a[2], length is
3, normal direction). here “…2” means end with a[2], and obviously we
should let “2…” means “start with”.
Some examples:
a[2…, 3] == a[2,3] -> [3,4,5]
a[2…, -3] == a[2,-3] -> [3,2,1]
a[…2, 3] -> [1,2,3]
a[…2, 3] -> [5,4,3]

This again is not possible, ruby ranges require a start and an end
(and ruby has no infinite structures) Changing the behavior for Array
only is not possible without changing Range, which would require an
languagewide change for a construct that is quite hard to read. (keep
in mind that String and tons of other classes share the behaviour of
Array in this regard)

2.Now we have: a[2…3] and a[2…3] to discribe a closed interval and a
semi-open interval. I think we should provide an easy way to discrible
any kinds of interval, may be like this:
2…4 means 2,3,4
[2…4) means 2,3
(2…4] means 3,4
(2…4) means 3
the way above may be not beautiful enough, but the function is
required i guess.

no, this again is a request to change Range in a really non-ruby
way. If you want a messy way to do such things, use [*]

[*(2…4)]

[2, 3, 4]

[*(2…4)]

[2, 3]

Moreover, I guess a[3…1] should means [4,3,2]. it is just the
semantic of “from…to”

Ranges build on the #succ method, the starting-element has to be <=
the end-element.

3.Some much more ideas:
a[i if odd?(i)] should be [2,4]
a[[1,3,3,4]] should be [2,4,4,5]
a[[1,3…4]] should be [2,4,5]
a[:]{|a[i]|, odd?(a[i])} should be [1,3,5], the block works as a
filter of the result.

class Symbol
def to_proc
Proc.new { |*args| args.shift.send(self, *args) }
end
end

class Integer; def odd?; self % 2 != 0; end; end

a.select(&:odd?)

[1, 3, 5]

a.reject(&:odd?)

[2, 4]

I won’t comment on the other notations since i simply can’t grasp
them. I am in no way an mathematician, but i am convinced that ruby
should be very simple and easy to understand. Especially constructs
that are used very often.

One could however propose to allow negative ranges, at least when the
content responds to #pred… i think this has been brought forward
quite often, but nobody has done an implementation of it so far.
Symbol#to_proc and Integer#odd? will be available with ruby1.9 as far
as i am informed…

^ manveru

ÍõÇ« wrote:

a[[1,3…4]] should be [2,4,5]

The #values_at method is useful for this:

irb(main):001:0> a = (0…9).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
irb(main):002:0> a.values_at(1…3, 5…7)
=> [1, 2, 3, 5, 6, 7]
irb(main):003:0> a.values_at(1…3, 5, 7)
=> [1, 2, 3, 5, 7]

On 1/26/07, Michael F. [email protected] wrote:

One could however propose to allow negative ranges, at least when the content responds to #pred...

There is no #pred (yet?) :frowning: http://rcrchive.net/rcrs/6

i think this has been brought forward

quite often, but nobody has done an implementation of it so far.
Symbol#to_proc and Integer#odd? will be available with ruby1.9 as far
as i am informed…

^ manveru

And what about the combination of all above?
(Some ideas come from the grammar of matlab. Its array’s interface
is great.)

Robert

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