Question about array.each{|x| delete x}

[Frisco Del Rosario]

myArray = [1, 2, 3]

puts myArray

myArray.each {|x|
if x == 1
then puts "one"
elsif x == 2
then
myArray.delete x
elsif x == 3
then puts "three"
end
}

puts myArray

The output of the above is:
1
2
3
one
1
3

And my question is "why isn't it 1 2 3 one three 1 3?". What if I wanted
to make it so?

 

[Peña, Botp]

From: Frisco Del Rosario [mailto:[email protected]]=20
# "why isn't it 1 2 3 one three 1 3?".=20

a delete (of some element) on an array will really be deleted, ergo, the =
elements will rearrange/move to logically occupy that deleted space.

eg,
b=3D[1,2,3,4,5]
#=3D> [1, 2, 3, 4, 5]
b.delete 2
#=3D> 2
b
#=3D> [1, 3, 4, 5]

also, array#delete(obj) will delete all elements eql to obj. see below.=20
now, if you combine these behaviours while walking the array itself, =
expect some surprises if you're not ready

maybe if you show the index, ruby can help you, eg

a=3D[1,2,3,1,1,4]
#=3D> [1, 2, 3, 1, 1, 4]
a.each_with_index{|x,i| a.delete x if x=3D=3D1; puts "#{i} -> #{x}"}
0 -> 1
1 -> 3
2 -> 4
#=3D> [2, 3, 4]


# What if I wanted to make it so?

there are many better ways, but i will just modify your sample,

myArray =3D [1, 2, 3]
puts myArray
myArray.delete 2 #here i delete 2 first
myArray.each {|x|
if x =3D=3D 1
then puts "one"
elsif x =3D=3D 3
then puts "three"
end
}
puts myArray

1
2
3
one
three
1
3

kind regards -botp

 

[tragomaskhalos]

myArray = [1, 2, 3]

puts myArray

myArray.each {|x|  
if x == 1
  then puts "one"
  elsif x == 2
    then
    myArray.delete x
  elsif x == 3
    then puts "three"
  end  
  }

puts myArray

The output of the above is:
1
2
3
one
1
3

And my question is "why isn't it 1 2 3 one three 1 3?". What if I wanted
to make it so?

I just dup, like this:
myArray.dup.each {|x| ... delete from (original) myArray in
here .... }

I'm sure there are more elegant solutions, and it's a bit pants from a
performance perspective for large arrays, but it works for me.

 

[Robert Klemme]

From: Frisco Del Rosario [mailto:[email protected]]
# "why isn't it 1 2 3 one three 1 3?".

a delete (of some element) on an array will really be deleted, ergo, the elements will rearrange/move to logically occupy that deleted space.

eg,
b=[1,2,3,4,5]
#=> [1, 2, 3, 4, 5]
b.delete 2
#=> 2
b
#=> [1, 3, 4, 5]

also, array#delete(obj) will delete all elements eql to obj. see below.
now, if you combine these behaviours while walking the array itself, expect some surprises if you're not ready

maybe if you show the index, ruby can help you, eg

a=[1,2,3,1,1,4]
#=> [1, 2, 3, 1, 1, 4]
a.each_with_index{|x,i| a.delete x if x==1; puts "#{i} -> #{x}"}
0 -> 1
1 -> 3
2 -> 4
#=> [2, 3, 4]


# What if I wanted to make it so?

there are many better ways, but i will just modify your sample,

myArray = [1, 2, 3]
puts myArray
myArray.delete 2 #here i delete 2 first
myArray.each {|x|
if x == 1
then puts "one"
elsif x == 3
then puts "three"
end
}
puts myArray

1
2
3
one
three
1
3

kind regards -botp

Well, you can as well do

myArray = [1, 2, 3]

puts myArray

myArray.delete_if {|x|
if x == 1 then
puts "one"
elsif x == 2 then
true
elsif x == 3 then
puts "three"
end
}

puts myArray

Note, this works because puts returns nil.

But I'd prefer using case

myArray.delete_if do |x|
case x
when 1
puts "one"
when 2
true
when 3
puts "three"
end
end

Cheers

robert