I have an array that I want to iterate over and delete some of the elements. This doesn't work:
a = [1, 2, 3, 4, 5]
a.each do |x|
next if x < 3
a.delete x
# do something with x
end
a #=> [1, 2, 4]
I want a to be [1, 2]. How can I get around this?
a.delete_if { |x| x >= 3 }
See method documentation here
Update:
You can handle x in the block:
a.delete_if do |element|
if element >= 3
do_something_with(element)
true # Make sure the if statement returns true, so it gets marked for deletion
end
end
x if it gets deleted. Should I put that in the block?
reject!.
reject! will return nil if no elements were rejected, while delete_if returns the original array.You don't have to delete from the array, you can filter it so:
a = [1, 2, 3, 4, 5]
b = a.select {|x| x < 3}
puts b.inspect # => [1,2]
b.each {|i| puts i} # do something to each here
.select returns a new ruby object which will use more memory. See this example pastebin.com/23e10bKy
I asked this question not long ago.
Deleting While Iterating in Ruby?
It's not working because Ruby exits the .each loop when attempting to delete something. If you simply want to delete things from the array, delete_if will work, but if you want more control, the solution I have in that thread works, though it's kind of ugly.
each effectively iterates by using the index. So if you delete, the indexes are different, and the next iteration will use the new indexes. Try this: arr = [1,2,3,4,5,6]; arr.each_with_index {|e,i| p [arr, e, i]; next if e < 3; arr.delete e }. When item 3 is reached, the index is 2. After 3 is deleted, the next iteration increments index to 3, and the item is 5. So 4 is skipped. 6 is skipped for the same reason.Another way to do it is using reject!, which is arguably clearer since it has a ! which means "this will change the array". The only difference is that reject! will return nil if no changes were made.
a.delete_if {|x| x >= 3 }
or
a.reject! {|x| x >= 3 }
will both work fine.
