--- title: partition, destructured assignment, and quicksort! in ruby slug: partition-destructured-assignment-and-quicksort-in-ruby published_at: 2021-11-24 14:00:05 +0000 updated_at: 2026-03-04 20:13:51 +0000 summary: description: partition, destructured assignment, and quicksort! in ruby Partition docs: https://apidock.com/ruby/v2_5_5/Enumerable/partition Best HTTP client article: https://www.scrapingbee.com/blog/best-ruby-http-clients/ Random quicksort visualization: https://visualgo.net/en/sorting Starwars API: https://swapi.dev/ Faraday docs: https://lostisland.github.io/faraday/usage/ Follow https://twitter.com/collin_jilbert tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, rails, javascript] views: 364 author: CJ Avilla url: https://www.cjav.dev/videos/partition-destructured-assignment-and-quicksort-in-ruby youtube_url: https://www.youtube.com/watch?v=6vc7jSJEJDU youtube_id: 6vc7jSJEJDU embed_url: https://www.youtube.com/embed/6vc7jSJEJDU thumbnail_url: https://i.ytimg.com/vi/6vc7jSJEJDU/hqdefault.jpg type: video --- # partition, destructured assignment, and quicksort! in ruby *Published: November 24, 2021* *Views: 364* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=6vc7jSJEJDU) [![partition, destructured assignment, and quicksort! in ruby](https://i.ytimg.com/vi/6vc7jSJEJDU/hqdefault.jpg)](https://www.youtube.com/watch?v=6vc7jSJEJDU) ## Description partition, destructured assignment, and quicksort! in ruby Partition docs: https://apidock.com/ruby/v2_5_5/Enumerable/partition Best HTTP client article: https://www.scrapingbee.com/blog/best-ruby-http-clients/ Random quicksort visualization: https://visualgo.net/en/sorting Starwars API: https://swapi.dev/ Faraday docs: https://lostisland.github.io/faraday/usage/ Follow https://twitter.com/collin_jilbert ## Transcript hey what's up welcome back so a couple weeks ago at rubyconf i met colin right here colin gilbert and uh he taught me about this new method that's available on the enumerable module called partition and what it does is you can call this on some collection and pass it a block and that'll return two separate arrays where the elements in one array will be when the block evaluates to true and the other array when the block evaluates to false there's another similar method here called group by but i wanted to dig in today into this partition method but i want to just dig into and play around with this partition method it's kind of fun and if you've never worked with it before um there's a couple like cool things you can do with it so suppose we have some input that has this array with um maybe like six elements or something and you want to just split it up so that you have all of the even elements and all the odd elements so we might say like even and odd is equal to input.partition and we want to pass it a block where it'll evaluate for each element in the block and we can say like if the element is even then we want that to be in our first array and if it's otherwise we're gonna put it in the second array so if we just like print out like even here is even and odd is odd then we'll see what we're talking about so if we run this ruby partition then we get out the even elements from the left side and the odd elements on the right side so that's one way to sort of like separate out the two we could change our block here so that it we're separating them out in a different way so instead what we could do is say maybe we want the elements that are less than three to be on the left side and the elements that are greater than or equal to three to be on the right side and so then what we get is this one two on the left and one two three four five six on the right kind of cool there are other uses for this but one thing i wanted to talk about is this destructured assignment thing that's going on on the left hand side so we're technically like creating this two variable two variables on the left right even and odd so if we didn't if we didn't do that if instead we said just like output or something and then we printed out output then we'll see that we actually get back an array that has two elements so this array has two elements one two those are the two elements in the array all right so first let's take a look at that destructured assignment thing and try to understand what's going on so if we had maybe like two variables a and b and we were assigning into that i don't know like uh x and y right and then down here we just wanted to print out like a is a and b is b then what might you expect to happen right um well first of all the first element in the array on the right-hand side is going to be assigned to the first variable that's on the left-hand side the second element is going to be assigned to the second variable so this is called like a destructured assignment i think and so what we can do is we can run our partition method again and now we can see that a is x and b is y but now suppose for a second that we actually had a third element in our array what do you think is going to happen right is where is z going to go if we only have two variables on the left and three elements in the array on the right hand side where do you think z might go well it turns out that z just gets dropped on the floor it's not assigned to anything because there's no slot for it to go into and so right now the way that we've written this we're really just collecting up the first element and the second element now ruby has the splat operator which allows us to sort of collect up more of those so if instead of just doing b here if we do star b or the asterisk before the b asterisk is like hard word to say then the first element this is also like a really common tool in like lisp where you'll have like a head or tail and so in this case the head meaning the first element in the collection on the right hand side is the value x and then the tail meaning b that's going to be like an array of all of the rest of the elements so let's take a look at how this works so now b is actually going to be an array so here we see like a has the value x and b is actually y and z the array of y and z so that is the tail there's another way we can do this too is we can put a splat operator in the front and say like give me everything except the last element so this works also so now b is going to be z and a is x and y this is like really helpful for building recurs some like recursive things but um yeah i just wanted to talk about that destructured assignment i think you can you can yeah so like you can even do like if we had x y z a b c you can even have like okay give me the last two elements and then put the rest in the front so you can kind of you can kind of put these on either end um if we do c here then yeah now we can see that like b is b and c is c because um c is pointing at the last element in the array b is pointing at the second to last element in the array and a is grabbing everything from the front forward now if again we switch this to be having c contain the rest of the elements then a will be x b will be y and c is going to be the array for the tail so the rest of the collection so if we run this again we see x y and then z abc right as uh the collection there so that's kind of like how you can think about do structured assignment this can also be useful as you're like iterating over lists of things uh the arguments into the block kind of behave in a similar way so you can use that splat operator that can be kind of handy all right back to partition back to partition so one one cool thing that we can do with partition is suppose we have like some api results so let's actually just like fetch some stuff from um the star wars api so we say require faraday um what we can do is instead of that being our input we can say that response is faraday.get um what is this swappy.dev api people and this will give us back some data so if we p response here and run our code we should be hitting the star wars api um and this is kind of just like a playground test api and we got back a bunch of data but i wanted to say like number one why i'm using faraday so there's this article here on scrapingb.com that goes through and evaluates several different ruby clients that make basically http clients and uh one that i've used for a really long time is called rest client uh i've heard of http party not a yeah whatever like i haven't used this a ton i haven't used http.rb net http is in the standard library this is like a recommended thing if you're building a client library that's going to interact with http but in practice faraday tends to be a great option it's not the fastest when you're making get requests it does pretty good for post requests they're i mean the the repo has lots of downloads and in millions and there's lots of stars at the end of the day it's all about your developer experience it's like how happy you are when you're writing ruby and net http pretty tricky to get right and uh yeah not a huge fan of working with it but if you are building a client library you don't want it to depend on other things and so yeah you can use that as part of the standard library so that was a big takeaway from this okay so we've got our response back from the api and this gives us a bunch of people that are available in the star wars api so if we look closely in here we see the name luke skywalker so luke skywalker is someone that was returned we also see some height and some mass so suppose for a second that we wanted to build a spaceship but we uh inside of the spaceship there's only a door that allows people to enter the door who are a certain height or shorter and so maybe what we can do is use the partition method on the results from this api call to separate out the characters who would fit through the door and the characters who would not fit through the door so 172 centimeters whatever so like i think what we can do is say like response.body we want to json parse this um i think there's ways to configure faraday so it does this by default um but let's just say our data is the parse json from that response body and then we want to say like i don't know results are data at results and what we want to do is we want to partition those so we want to say like results.partition and we're getting back a character so we'll say this is a character and if the character's height is um less than 160 centimeters or something that should include luke skywalker so then we'll say like uh now we have like short uh and tall is kind of the separation of the people where the cutoff between short and tall is 160 centimeters and then we'll just print out short and print out actually like i think we what we want to do is actually um uh iterate over short dot yeah like we want to map this so that we see their name so let's just see what this looks like also height i noticed i don't know we'll we'll see an issue here so if we run this again okay so we got an error it says partition in partition rb on line 8 in the less than operation the comparison of string with 160 failed so uh this right here height is returned from the api as a string i don't know i don't know why but we can just like convert that into an integer and hope that no characters come back with non-integer heights but okay so we see r2d2 leia and r5d4 are all the right height i don't know let's see if we make it one 180 180 centimeters we don't want just droids and leia uh run it again okay so now we get luke leia owen a bunch of people so this is these are the folks that are short enough to go uh who are allowed to go on the trip so we'll say like um like what is that passengers and everyone else will be left behind and we can do the same thing so tall dot map and we'll pull out the name and let's just see what happens all right so the passengers that are coming aboard is luke skywalker c3po r2d2 leia owen barrow i guess owen is owen wait is this his wife daughter i don't know who is baru i don't know that character r5d4 and then who was left behind darth vader thank god right uh biggs dark lighter and obi-wan kenobi oh we can't leave obi-wan that's all right whatever so this is one way that you might use partition uh to like separate out results so here we're like digging into the character object that came back and doing some analysis on that and that gives us like short and tall cool the next thing i wanted to talk about with partition that's super cool is this algorithm called quick sort so quick sort is an algorithm that allows you to sort of divide and conquer so suppose you had a bunch of elements and you wanted to sort them um one way that you could do that is like find a pivot point and anything that is less than that pivot point you um put it before and everything that's greater than the pivot point you put it after so this is sort of a visualization of how that happens but what i wanted to do is like try to do a quick sort implementation where the partition is this partition method and we randomly find an element and we use that as our pivot point and we move the half the things to the left half the things to the right and then we can like recursively um work our way down so let's try to do that i'm just going to comment this stuff out and then let's say okay so suppose we have some like input that is like maybe they're ages i don't know 33. so now what we want to do is make some method that like sorts these so we could just call input.sort uh that's super boring right like this is what we're kind of going for is seeing 2 7 23 32 33 whatever but what we want to do is make some method called quick sort or no this is uh is it quick sort random quicksort whatever we'll just make our method called sort that takes input and its job is going to be like okay we want to randomly pick some pivot point um so we're going to say like the pivot is going to be input.sample so input.sample is a way of saying like our sample is like saying give me a random number from here so if we look at this like let's open up pry and we can say something like one two three four five six seven eight dot sample and that will just pull out a random number and give us back the random number happens to be seven lucky number seven several times uh okay so uh if you were a gambler and this was your lucky number that would be pretty crazy because you would have hit five out of what is that six five out of nine five out of seven shots um okay cool so this is a way that you can grab your random pivot uh great so we've got our pivot this is going to be the number where we want to partition around that pivot so we're going to say we've we've we've picked some random number let's say the number is 23. what we're going to do is say and as we partition the results we're going to partition them such that the numbers in the in the list that are less than 23 go on the left and anything 23 or greater goes on the right and then we will um we will recur on the those results okay so what we want to do is we're going to say like left and right are equal to input.partition and we're going to pass in like whatever the numbers are and then we are going to say like if num is less than pivot then included in the left otherwise included in the right and then what we want to do is we want to return the sorted left plus the sorted right okay so this is going to be our recursion this is where we're like actually calling ourself again but left here should definitely be a smaller amount than what the input was and right should be a smaller amount than what the input was and so we are going to get uh ultimately we're going to like be passing in arrays that are smaller and smaller and smaller until we start getting return values where things are like sorted out so at the base case here so we need a base case so that we can we can actually return so the base case is going to be if the input is if we get an input that is an empty list or a list with one element then we want to return so we're going to say return input if input.length is less than or equal to 1. so this is our this is sort of our base case that we need to add and then otherwise i think we can say sort input and just see what happens uh i guess we want some output right uh p sort input and there we go we got 2 23 32 whatever so like to see what's happening here let's do puts left is left and right is right just to see if we can like get a better breakdown so in the beginning right we our partition oh we it's also let's show our pivot too so our i guess like in the middle we'll just say like uh p for our pivot is pivot and that should be random right because we're using sample okay so our pivot in this case was 98 so anything less than 98 ends up in the left and anything 98 or greater ends up in the right so here our pivot is 63 and so like this first call in this first call our right hand side ended up being 98 and 101 but also so in the second call we were only considering this left hand side because recall that we like recurse and we call sort again first with the left then we concatenate that with what's on the right so when we see 63 here and we only on the right hand side we only see 65 63 we don't see 98 and 101 that's because this result that we're printing out is only for the recursion on this left side and so here's the numbers that are 63 or greater and everything less than 63 is on the left again now this next call is again being we're pivoting on a number that was randomly sampled from the left we get two and seven two two and seven we call it again with now we're calling with the right right-hand side so then like you kind of ultimately build up until you get back to um the return values that you concatenate all together and then you spit them out so that is uh i'm pretty sure don't don't correct me if i'm wrong i mean yes please do correct me if you know better than i do please leave a comment that says um that this is uh not whatever this is not quicksort but the algorithm and the idea and the concept of like pivoting and splitting and re like working your way back is uh definitely how i think about it so that's like a cool use of pivot also if you're curious about using faraday that thing that we used to make http requests you can go to their docs here and learn more about pulling out the status or the headers or the response body things like that um cool yep so that is the partition method a couple different use cases uh i really enjoyed it thanks colin so much for teaching me about that and yeah we'll see you later [Music] --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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