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Iteration With Each

4:51 with Jason Seifer

The while loop will print out an array and use a variable to increment and keep track of what it is printing out. As we're looping through each item in the array, we're using a specific pattern -- getting an item out of the array and working with it in a specific way. You could say that we're iterating over each item in the array. Ruby gives us ways to do this without writing a loop each time. The "each" method is commonly used to iterate over a collection of items, like an array.

Code Samples

Given the following array:

array = [0, 1, 2, 3, 4, 5]

We can use the each method to iterate over the individual items in the array:

array.each do |item|
  puts "The current array item is: #{item}"
end

The do...end is called a block. A block is a chunk of code you can pass into a Ruby method. What the each method does is to call your block once for each item in the array, and pass the item into the block as an argument. So the above block prints each item in the array on its own line.

The block can also be written on one line:

array.each {|item| puts "The current array item is: #{item}"}

It is conventional to write blocks using the do...end syntax for multiple lines of code in the block and the braces {} syntax for single line code blocks.

We can also manipulate items inside of an each block:

array = [0, 1, 2, 3, 4, 5]
array.each do |item|
  item = item + 2
  puts "The current item + 2 is #{item}."
end

This will leave the original array unchanged.

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    [MUSIC] 0:00
    Let's talk about iteration in Ruby. 0:04
    Let's say that we had the following while loop that we were working with. 0:07
    The while loop will print out an array and use a variable to increment and 0:12
    keep track of what is printing out. 0:16
    As we're looping through each item in the array, we're using a specific pattern. 0:19
    Getting an item out of the array and working with it in a specific way. 0:24
    You could say that we're iterating over each item in the array. 0:29
    Ruby gives us a way to do this without writing a loop each time. 0:35
    The each method is commonly used to iterate over a collection of 0:39
    items like an array. 0:43
    Let's see how that works now using work spaces. 0:45
    So here we have an example array. 0:49
    It is a six-item array with the numbers zero through five. 0:51
    Now we've got this while loop that starts and goes through each item in the array. 0:56
    And then we can see on the bottom here, it prints out the numbers zero through five. 1:03
    Now let's go ahead and comment this out. 1:07
    And we do that by typing a pound on the front of each line that we want 1:12
    commented out. 1:17
    And a comment means that Ruby will ignore it when it goes to run the program. 1:19
    If we wanted to use the each method to iterate over this, 1:25
    we can do it pretty easily. 1:30
    We take our variable, which in this case is array, and then type a dot, 1:33
    the word each, and then we start a block 1:38
    using the do and end key words. 1:46
    Now, when we start a block, it's going to perform 1:51
    the statements inside the block on each item inside the array. 1:55
    Now when it does that, it goes into the block as an argument. 2:00
    So, using Ruby syntax, we send items into blocks as arguments with a pipe, 2:06
    the name of the variable that we want inside this block and another pipe. 2:14
    Now, we can do the same thing. 2:20
    In fact, I'm going to just copy and paste it here. 2:23
    And it's going to say the current item is item. 2:28
    Now, I'm gonna clear the screen on the bottom here and type ruby each.rb again. 2:32
    And you'll see it prints out the exact same thing, only this time, 2:37
    we used the each method to iterate over it. 2:41
    Now just like with other loops and blocks, we could use curly braces, or do and 2:45
    end, to do the iteration and it will do the same thing. 2:51
    And in fact, we could put this all on one line, if we wanted to. 2:57
    Now, let's go ahead and create another file. 3:04
    And we'll call this each_addition.rb. 3:09
    And what we're gonna do, we can actually take this here, we'll take the array, so 3:14
    that we have it set up. 3:19
    And let's check this out. 3:22
    We'll iterate over it again, array.each do |item|. 3:22
    And then we'll say, 3:28
    The current item + 2 is #(item). 3:32
    And let's go ahead and change item 3:38
    right here, item = item + 2. 3:43
    So we're gonna add two to each item inside of this array and then print that out. 3:48
    So I'm gonna clear my screen again. 3:55
    And we'll run that again. 3:59
    And it says, The current item + 2 is 2. 4:02
    Current item + 2 is 3, 4, 5, 6 and 7. 4:05
    But now, let's take a look at the array afterwards. 4:10
    We've set the item equal to the same item + 2, 4:17
    which is going to change the item inside of this block. 4:22
    But when we inspect the array again, the array is unchanged. 4:29
    That's because anything we do to the item inside of the block 4:35
    only applies to this variable, which is item, and 4:40
    it's a copy of what is in the array for each iteration. 4:45

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