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How would I modify (add/remove elements) an array while iterating over it and have the iterator be aware of it?

For example I would think this code:

a = "1234567890".split("")
a.each_with_index{|d, i|
 if d.eql?('5')
  a.delete_at(i)
  a.insert(i, ['A', 'B', 'C'] )
 end
print d
}

would produce: 1234ABC67890 but instead produces 1234567890

Is there a workaround or different method to make this work?

(I know this example is pretty simple example but I am doing some complicated text processing where I need to insert some text when I hit a key word. I do a bunch of functions before and after I would do the expansion so doing the insert outside of the each loop [aka map!] would really complicate my code)

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4 Answers 4

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1

Actually, your code works, you just need to replace print d with print a[i] since what you're printing is the variable d not the actual array element at index i

Rather than deleting and inserting, why not change the element on that index? 

    a = "1234567890".split("")
    a.each_with_index{|d, i|
     if d.eql?('5')
      a[i] = ['A','B','C']
     end
    print a[i] #a[i] rather than d, since d contains the old value
    }

or

 ...
if d.eql?('5')
   a[i] = ['A','B','C']
   d = a[i]
end
print d

Deleting/Inserting on an Array during iterations is discourage since it may cause headaches haha... Resort to other methods if possible :)

Note: I've just used the current logic in your code based on my understanding, and the given desired output

the array will become [1,2,3,4,['A','B','C'],6,7,8,9,0] and not [1,2,3,4,'A','B','C',6,7,8,9,0]. If you want the other, just leave a comment :)

If what you want is just to change a value in the string, you can just use .tr or .gsub to do the job

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4 Comments

you are correct the outcome of code will be [1,2,3,4,['A','B','C'],6,7,8,9,0] but the desired outcome is [1,2,3,4,'A','B','C',6,7,8,9,0]... I guess I need to write an method to expand array into multiple parameters (aka a.insert[i, 'A', 'B', 'C']
the solution is just simple... you can just do an .insert 3 times :) but you have to start backwards. e.g. a.insert(i,'C');a.insert(i,'B');a.insert(i,'A'); since insert will displace the other elements to the left
to the right I mean, If you're gonna view an array growing to the right :)
actually I used the splat operator: a.insert[i, *other_array] not sure why I didn't think of it sooner -thanks
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Here is one option. If you want to return array then remove join otherwise keep it to return a String

a = "1234567890".split("")
a.collect! {|i| i == '5' ? ['A', 'B', 'C'] : i }.flatten!.join #=> "1234ABC67890"
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0

Inserting and deleting while iterating is best avoided. Some problems disappear however when iterating in reverse order: 

a = "1234567890".split("")
a.reverse_each.with_index{|d, i|
 if d.eql?('5')
  a.delete_at(i)
  a.insert(i, ['A', 'B', 'C'] )
 end
}
puts a.join # => 12345ABC7890
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0

You can't in general modify an Enumerable while iterating over its members. In most such cases, you need to construct a new Enumerable as you go.

b = []
a.each_with_index do |d, i|
  if d.eql?('5')
    b << 'A' << 'B' << 'C'
  else
    b << d
  end
end
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