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Ruby Collections

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Removing Items From Arrays

3:43 with Jason Seifer

So far while working with arrays, we've learned how to add and access the items inside. Now it's time to learn how to remove items in arrays.

Code Samples

Let's assume we have the following array:

array = ["milk", "eggs", "bread", "ice cream", "carrots", "potatoes"]

To access and remove the last item in the array, we can use the pop method: 

last_item = array.pop

The last_item variable will now contain the string potatoes. The array now looks like this:

["milk", "eggs", "bread", "ice cream", "carrots"]

To access and remove the first item in the array, we use the shift method: 

first_item = array.shift

The first_item variable now contains the string milk. The array now looks like this:

[ "eggs", "bread", "ice cream", "carrots" ]

We can use the drop method to take out a number of items from an array. The drop method's argument is the number of items to remove from the front of the array.

ice_cream_carrots = array.drop(2)

Similar to the unshift method, which adds to the beginning of an array, the shift method removes from the beginning of an array:

item = array.shift

The item variable now contains the string "eggs" and our array looks like this:

[ "bread", "ice cream", "carrots" ]

Let's add "potatoes" to the end of our array:

array.push("potatoes")

The array now contains:

["bread", "ice cream", "carrots", "potatoes"]

The slice method takes two arguments and removes and returns items from the array. The first argument is the index in the array, and the second argument is the number of items:

first_three_items = array.slice(0, 3)

Now, the first_three_items variable contains the following array:

["bread", "ice cream", "carrots"]

The array variable is now a single element:

["potatoes"]

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    Now that we can add things to arrays and get things back out of arrays, 0:00
    wouldn’t it be useful if we could also remove things from arrays? 0:04
    Let’s take a look at how that works now using workspaces. 0:09
    Okay, so let's launch irb again inside of a Ruby workspace. 0:13
    And we'll set up our grocery_list array. 0:17
    So we'll give this a few different items here. 0:20
    All right, now if we want to get to the last item in this array, 0:30
    let's go ahead and assign that to a variable called last_item. 0:34
    And we'll use the pop method, which returns the last item in the array, 0:40
    and removes it from the original array. 0:45
    That's the big difference between the last method and the pop method. 0:48
    So if we look at the last item here, we'll say grocery_list.pop. 0:53
    Now our variable last_item has the string "potatoes", but 0:58
    if we look in our grocery_list this time, it is now lacking "potatoes". 1:03
    Similarly, there's another method called shift, which returns the first item. 1:08
    So we'll look at the grocery_list array here. 1:14
    And we'll call the shift method on it. 1:17
    Now, it we look at our first item, it contains the string "milk". 1:20
    And if we take a look at our grocery_list, 1:25
    it now only has four items in it, "eggs", "bread", "ice cream", and "pie". 1:27
    So we've already done some shopping here. 1:32
    Now let's say we wanted to take two items off of this grocery_list. 1:35
    Let's create a variable called drop_two_items. 1:40
    And we'll say grocery list, the method drop, and the number 2. 1:45
    Now let's go ahead and look at our drop_two_items variable. 1:50
    It contains "ice cream" and "pie", the last two items in the array. 1:54
    Now let's take a look at our grocery_list. 2:00
    The grocery list was not modified by the drop method and 2:03
    still has everything inside of it. 2:07
    Gonna clear my screen here. 2:10
    Let's take a look at our grocery_list. 2:12
    Now here's another cool thing. 2:14
    If we want to add onto the beginning of the array, just like 2:16
    we took from the beginning of the array earlier, we could use the unshift method. 2:19
    So, let's say, grocery_list.unshift, and we'll give that "milk". 2:25
    Now our grocery_list has "milk" on the front of it. 2:31
    And let's go ahead and put "potatoes" back on there. 2:36
    All right, now we have a pretty decent grocery list to work with. 2:40
    I'm going to clear my screen again, and that's our grocery list. 2:42
    And let's say we wanted the first three items from this grocery list. 2:47
    We could use the slice method. 2:52
    So let's say, first_three_items = grocery_list.slice. 2:54
    Now we give it the index, which is 0, and the number of items we want, which is 3. 3:00
    Now first_three_items contains "milk", "eggs", and "bread", 3:07
    and our grocery_list was unmodified by the slice command. 3:12
    Now we could give it any index we wanted. 3:18
    So we could say new_list is grocery_list.slice and then any index. 3:20
    Let’s give it the index of 2. 3:27
    And say we only want 2 items, and that's gonna be "bread" and "ice cream". 3:29
    Now that's what our new list contains as well. 3:35
    Try removing things from arrays now on your own, using Workspaces. 3:38

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