I have this code and I don't know why it doesn't give me the correct answer
list = [1]
a = [0,0,2,3,4]
for n in a
if n!= 0
list.push(n)
a.delete(n)
end
end
p list => [1,2,4]
p a => [0,0,3]
I don't understand why number didn't get added to list. When I tried to only use 'push' and not 'a.delete' I got the correct answers
list = [1,2,3,4]
a = [0,0,2,3,4]
What is going on?
Rule number one of iterating collections: don't change the collection you're currently iterating!.
A quick fix would be to iterate a copy of the collection.
list = [1]
a = [0,0,2,3,4]
for n in a.dup # here, a copy
if n!= 0
list.push(n)
a.delete(n)
end
end
list # => [1, 2, 3, 4]
a # => [0, 0]
list # => [1, 2, 3, 4] automatically in your editor or you do edit this way? As I am running ST2 where output comes in different window, and I need to copy there from and paste it to here,which causes slower posting :)see the output carefully:
list = [1]
a = [0,0,2,3,4]
for n in a
if n!= 0
list.push(n)
a.delete(n)
p list,a
end
end
Output:
[1, 2]
[0, 0, 3, 4]
[1, 2, 4]
[0, 0, 3]
So when your loop deleted 2, which was in the 3rd item before deletion, 3 comes into that position. And as the loop completed the 3rd item processing,it will jump to the take next item from the collection,which is 4. This is how item 3 will be skipped. As after deletion all your item will be shifted from right to left. Look below for more clarity to see what is going on inside the loop and state of collection a after each delete.
list = [1]
a = [0,0,2,3,4]
for n in a
if n!= 0
p n
i = a.find_index(n)
list.push(n)
a.delete(n)
p a[i]
p "-" *8
end
end
output:
2
3
"--------"
4
nil
"--------"