Hash Methods

Just like strings and 0:01 numbers, Ruby gives us a lot of methods we can use to work with hashes. 0:02 These methods can operate on keys and values at the same time. 0:08 Let's take a look at how some of them work now, using work spaces. 0:13 Okay, now that we know how to create and work with hashes, let's go ahead and 0:17 start learning about some different hash methods. 0:21 And I'm gonna create a file for this and we're gonna call it hashmethods.rb. 0:24 Now let's go ahead and set up a hash to work with. 0:30 And we'll have the keys of hash, item, and that's bread. 0:35 And we only want one. 0:43 And the brand is Treehouse Bread Company. 0:48 Okay, now, let's go ahead and just print out the hash. 0:52 Let's just run this and make sure everything is working and nothing's crazy. 1:00 So click down into the console, and type ruby and then hash_methods.rb, 1:05 and there is a printout of our hash. 1:10 Now I'm gonna get these hash methods from the Ruby Hash documentation. 1:15 Some of the methods that we're going to look for here, the first one is length. 1:20 And that will return the number of key value pairs in the hash. 1:26 Let's go ahead and see how that works now. 1:32 And we'll just say hash dot length. 1:35 And print it out. 1:39 And let's run this again and see what happens. 1:43 All right, the hash has a length of three. 1:47 And you know what let's change that to print. 1:50 So it's all on the same line. 1:54 Clearing my screen on the bottom there with Ctrl+L, and there we go, 1:56 we have a length of 3. 2:01 Another neat method is something called invert and 2:02 that will transpose the keys and values into a new hash. 2:07 And let's go ahead and print that to the screen as well. 2:14 I'm gonna save that and run that again and now if we look, here's our original hash. 2:19 But when we run the invert method, it changes all the keys and values. 2:27 And it does not change the original hash. 2:32 The next method that we can take a look at is called shift. 2:38 Now if I click on the methods list here in the hash documentation. 2:43 This will remove a key value pair from the hash and 2:47 return it as a two item array with the key and value. 2:51 Let's go back to our workspace and see how that works. 2:56 So we're gonna print out the hash after shifting it as well. 3:05 And we can use the inspect method to print out the hash. 3:14 Let me clear out my screen on the bottom again, with Ctrl + L and run this again. 3:18 Now, we've called hash.shift and this returns item and 3:24 bread in an array form, but are we really sure it's an array? 3:28 Let's go ahead and call the inspect method on that to make sure. 3:33 So when we run that again, we can see this comes back as an array, 3:38 and our hash now does not have the item Item is the key. 3:44 Let's go ahead and put the item back in the hash. 3:49 So we'll say item, hash, item is bread. 3:52 Now let's go back and look at some more methods. 3:58 The last method that we're gonna look at is called merge. 4:01 Now merge gives an argument of another hash and returns a new hash. 4:04 That sounds a little confusing, so let's go ahead and see how it works. 4:10 And we can just print this out now. 4:15 So here's our hash, let's print that out. 4:21 And now, let's print this out and merge it with a couple other hashes. 4:27 Now we call the merge method and then we pass in another hash. 4:38 And then we'll go ahead and 4:49 print the original hash out again, just to see what it looks like. 4:50 Clear my screen since this is getting to be a lot of output and we'll run it again. 4:55 So now we've printed out Merged with this particular hash and 5:01 what we get back is a new hash. 5:07 You know what, that's a little hard to read. 5:10 Let's change this to puts and run it again. 5:11 So here's our original hash. 5:17 Now we merge it with calories of 100 and we get back this hash, 5:19 which contains another hash with calories of 100 added on to the original hash. 5:25 But, if we look back at that original hash, it does not have the calories key. 5:34 This is because merge will create a new hash. 5:39 Now you might wonder what would happen, 5:45 if we called merge with a key that already exists inside the hash. 5:47 Let's go ahead and see what happens. 5:52 And we'll just merge that with a different item name. 5:59 Now let's clear the screen here and run it again and see what happens. 6:12 Now when we do it, we'll see that the new hash comes back 6:16 with only one key of item which points to eggs. 6:21 Which is the last thing that we called in with merge. 6:26 When merge has a conflicting hash key, the hash that's sent into merge 6:30 receives precedence and will overwrite the existing key value pair. 6:36 Using the documentation linked in the teacher notes section of this video, try 6:41 looking up and practicing with different hash methods on your own using workspaces. 6:46