Asp Forum - big array, problems with deleting all empty items

Simon Schuster

10/15/2007 5:42:00 PM

it seems that I have to run it a couple different times for it to
work.. array.length = 16576, if that could be a potential problem. if
it is, how do I work around it?

077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
080:0> array.each_with_index { |x,y|
array.delete_at(y) if x.empty? == true
}

still leaves me with plenty of empty array items
080:0> array[-3]
""

8 Answers

Robert Klemme

10/15/2007 6:04:00 PM

On 15.10.2007 19:41, Simon Schuster wrote:
> it seems that I have to run it a couple different times for it to
> work.. array.length = 16576, if that could be a potential problem. if
> it is, how do I work around it?
>
> 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
> 080:0> array.each_with_index { |x,y|
> array.delete_at(y) if x.empty? == true
> }
>
> still leaves me with plenty of empty array items
> 080:0> array[-3]
> ""

Your bug is in the loop: you iterate and delete at the same time which
will likely yield strange results (as you observe). Why don't you just do

array.delete_if {|x| x.empty?}

Btw, empty? == true is quite dangerous because in Ruby "true" is not the
only valid value for true.

Apart from that it seems your code is pretty inefficient since you do a
lot copying around. I'd rather do this

ar = []
File.foreach("text.txt") do |line|
line.chomp!
ar << line unless line.empty?
end

Cheers

robert

James Gray

10/15/2007 6:09:00 PM

On Oct 15, 2007, at 12:41 PM, Simon Schuster wrote:

> it seems that I have to run it a couple different times for it to
> work.. array.length = 16576, if that could be a potential problem. if
> it is, how do I work around it?
>
> 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }

That's better written as:

lines = File.readlines("/text.txt")
lines.each { |l| l.chomp! }

> 080:0> array.each_with_index { |x,y|
> array.delete_at(y) if x.empty? == true
> }

And this can be as simple as:

lines.delete_if { |l| l.empty? }

However, I would switch strategies and only add the lines you are
interested in to begin with:

lines = Array.new
File.foreach("/text.txt") do |line|
line.chomp!
lines << line unless line.empty?
end

I hope that helps.

James Edward Gray II

7stud --

10/15/2007 6:14:00 PM

Simon Schuster wrote:
> it seems that I have to run it a couple different times for it to
> work.. array.length = 16576, if that could be a potential problem. if
> it is, how do I work around it?
>
> 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
> 080:0> array.each_with_index { |x,y|
> array.delete_at(y) if x.empty? == true
> }
>
> still leaves me with plenty of empty array items
> 080:0> array[-3]
> ""

Try running this code:

arr = [10, 20, 30, 40]

arr.each_with_index do |elmt, i|
puts elmt
arr.delete_at(i) if elmt == 20
end

As you can see that code tries to display every element in the array.
Does it succeed?

This convoluted code:

> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
> array.each_with_index { |x,y|
> array.delete_at(y) if x.empty? == true
> }

can be done more directly doing something like this:

arr = []

IO.foreach("data.txt") do |line|
if line != "\n"
arr << line.chomp
end
end

puts arr

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

Konrad Meyer

10/15/2007 6:38:00 PM

Quoth Robert Klemme:
> On 15.10.2007 19:41, Simon Schuster wrote:
> > it seems that I have to run it a couple different times for it to
> > work.. array.length = 16576, if that could be a potential problem. if
> > it is, how do I work around it?
> >
> > 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
> > 080:0> array.each_with_index { |x,y|
> > array.delete_at(y) if x.empty? == true
> > }
> >
> > still leaves me with plenty of empty array items
> > 080:0> array[-3]
> > ""
>
> Your bug is in the loop: you iterate and delete at the same time which
> will likely yield strange results (as you observe). Why don't you just do
>
> array.delete_if {|x| x.empty?}
>
> Btw, empty? == true is quite dangerous because in Ruby "true" is not the
> only valid value for true.

But !!e.empty? == true will do the trick :D.

--
Konrad Meyer <konrad@tylerc.org> http://konrad.sobertil...

mortee

10/15/2007 8:56:00 PM

Robert Klemme

10/16/2007 4:36:00 PM

On 15.10.2007 20:38, Konrad Meyer wrote:
> Quoth Robert Klemme:
>> On 15.10.2007 19:41, Simon Schuster wrote:
>>> it seems that I have to run it a couple different times for it to
>>> work.. array.length = 16576, if that could be a potential problem. if
>>> it is, how do I work around it?
>>>
>>> 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
>>> 080:0> array.each_with_index { |x,y|
>>> array.delete_at(y) if x.empty? == true
>>> }
>>>
>>> still leaves me with plenty of empty array items
>>> 080:0> array[-3]
>>> ""
>> Your bug is in the loop: you iterate and delete at the same time which
>> will likely yield strange results (as you observe). Why don't you just do
>>
>> array.delete_if {|x| x.empty?}
>>
>> Btw, empty? == true is quite dangerous because in Ruby "true" is not the
>> only valid value for true.
>
> But !!e.empty? == true will do the trick :D.

I've seen the smiley but, frankly, I find this only moderately funny.
The reason is that there are too many people around that think comparing
boolean values is a great idea. This is at least superfluous and often
outright dangerous. Other people then will have to debug those bugs...

Cheers

robert

John Joyce

10/16/2007 9:16:00 PM

On Oct 16, 2007, at 11:40 AM, Robert Klemme wrote:

> On 15.10.2007 20:38, Konrad Meyer wrote:
>> Quoth Robert Klemme:
>>> On 15.10.2007 19:41, Simon Schuster wrote:
>>>> it seems that I have to run it a couple different times for it to
>>>> work.. array.length = 16576, if that could be a potential
>>>> problem. if
>>>> it is, how do I work around it?
>>>>
>>>> 077:0> array = File.read("/text.txt").to_a.each { |x| x.chomp! }
>>>> 080:0> array.each_with_index { |x,y|
>>>> array.delete_at(y) if x.empty? == true
>>>> }
>>>>
>>>> still leaves me with plenty of empty array items
>>>> 080:0> array[-3]
>>>> ""
>>> Your bug is in the loop: you iterate and delete at the same time
>>> which will likely yield strange results (as you observe). Why
>>> don't you just do
>>>
>>> array.delete_if {|x| x.empty?}
>>>
>>> Btw, empty? == true is quite dangerous because in Ruby "true" is
>>> not the only valid value for true.
>> But !!e.empty? == true will do the trick :D.
>
> I've seen the smiley but, frankly, I find this only moderately
> funny. The reason is that there are too many people around that
> think comparing boolean values is a great idea. This is at least
> superfluous and often outright dangerous. Other people then will
> have to debug those bugs...
>
> Cheers
>
> robert
>
Well, in this case it may be just naive.
In many languages you might have to do something like that.
No big deal.
Comparing a boolean method to a boolean value will only ever return a
boolean.
Can't go wrong.

If it is set up right it could be convenient if there is a chance of
a nil value, because nil == true returns false.
But the condition is still in .empty?

Stefan Rusterholz

10/17/2007 12:00:00 PM

comp.lang.ruby

big array, problems with deleting all empty items

Simon Schuster

Robert Klemme

James Gray

7stud --

Konrad Meyer

mortee

Robert Klemme

John Joyce

Stefan Rusterholz

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