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+---
+title: Hello, J! Sorting Some Strings
+route: /j-sorting
+date: 2020-04-01
+description: We'll learn a few fun features in the J programming language by sorting some strings.
+---
+
+<!-- Inconsolata monospace doesn't work too good with J's unicode boxes -->
+<style>pre code {font-family:monospace}</style>
+
+Following my previous [(1)](/j-fibonacci) posts [(2)](/j-pascal) on a fun little language called J (http://jsoftware.com/), I thought I'd do a quick writeup for some source code I provided in the [Khan Academy Alumni](https://www.khanacademy.org/about/alumni) slack channel.
+
+([They're](https://www.khanacademy.org/careers) hiring! [Stripe](https://stripe.com/jobs) is too!)
+
+Over the next few paragraphs we're going to sort some strings by length, and end up with a function that is 5 characters in length: `\:#&>` (really!)
+
+```
+   (\:#&>) ;: 'sorting strings by length'
+┌───────┬───────┬──────┬──┐
+│sorting│strings│length│by│
+└───────┴───────┴──────┴──┘
+```
+
+## Boxes of strings
+
+We can use the [`;: Words`](https://www.jsoftware.com/docs/help804/dictionary/d332.htm) verb to get a list of words in a string.
+
+```
+   'a'; 'tall'; 'cat'
+┌─┬────┬───┐
+│a│tall│cat│
+└─┴────┴───┘
+   ;: 'a tall cat'
+┌─┬────┬───┐
+│a│tall│cat│
+└─┴────┴───┘
+```
+
+The fancy characters around each word represent the fact that they are "boxed."
+
+We can [`> Open`](https://www.jsoftware.com/docs/help804/dictionary/d020.htm) boxes.
+
+```
+   > ;: 'a tall cat'
+a
+tall
+cat
+```
+
+We can get the number of items in a list (or a string - which is a list of characters) using the [`# Tally`](https://www.jsoftware.com/docs/help804/dictionary/d400.htm) verb.
+
+```
+   # 1 3 5
+3
+   # 'hello'
+5
+```
+
+We can compose these two operations with [`& Bond`](https://www.jsoftware.com/docs/help804/dictionary/d630n.htm) conjunction, which takes two verbs and returns a single verb.
+
+```
+   # & > ;: 'hello world'
+5 5
+   #&> ;: 'a tall cat'
+1 4 3
+```
+
+Now we are able to get the number of characters in each string.
+
+## Sorting and ranking
+
+[`\: Sort Down`](https://www.jsoftware.com/docs/help804/dictionary/d432.htm) is a powerful verb which sorts the left argument using the right argument for scoring (in descending order).
+
+For example, we can rearrange "hello" by giving `l` and `h` a score of 1 and 2 respectively, and giving `e` and `o` a score of 11 and 10 (respectively). `e` will then appear at the front of the result as it received the highest score.
+
+```
+   'hello' \: 1 11 2 2 10
+eollh
+```
+
+We can use this to sort our list of words, using the length of each word as its score.
+
+```
+   #&> ;: 'a tall cat'
+1 4 3
+   (;: 'a tall cat') \: 1 4 3
+┌────┬───┬─┐
+│tall│cat│a│
+└────┴───┴─┘
+   (;: 'a tall cat') \: #&> ;: 'a tall cat'
+┌────┬───┬─┐
+│tall│cat│a│
+└────┴───┴─┘
+```
+
+## Making things shorter
+
+We've successfully used the `;:`, `\:`, `#`, `&`, and `>` operators to piece together a working sort mechanism, but there's one flaw - we have to repeat `;: 'a tall cat'` twice 😱
+
+To alleviate this, we can use one of J's strongest features, [hooks](https://www.jsoftware.com/docs/help804/primer/hook.htm).
+
+In the following example, we'll take a list of numbers and add 7% to each of them. We may be inclined to write it like so:
+
+```
+   10 40 55 + 0.07&* 10 40 55
+10.7 42.8 58.85
+```
+
+Which reads, take the list `10 40 55` and apply `0.07&*` (remember [bond](https://www.jsoftware.com/docs/help804/dictionary/d630n.htm)?) to each item. Add the result to the list `10 40 55`.
+
+(Author's note: we also may be inclined to just multiply by 1.07 but that requires math).
+
+Hooks allow us to simplify this by simply leaving off one of the arguments.
+
+```
+   (+ 0.07&*) 10 40 55
+10.7 42.8 58.85
+```
+
+How does this work? J recognizes that we have two verbs within our parentheses (`+` and `0.07&*`) and combines them into a "[hook](https://www.jsoftware.com/docs/help804/primer/hook.htm)." When we place a single argument at the end, J **automatically applies it to both sides of the hook**.
+
+Put another way: `(f g) x <=> x f g x` for any two verbs `f` and `g` (don't forget your parentheses!)
+
+So, the following expressions are equivalent:
+
+```
+   10 40 55 + 0.07&* 10 40 55
+10.7 42.8 58.85
+   (+ 0.07&*) 10 40 55
+10.7 42.8 58.85
+```
+
+Let's circle back to our sorting mechanism before and see where we can apply this.
+
+```
+   (;: 'a tall cat') \: #&> ;: 'a tall cat'
+┌────┬───┬─┐
+│tall│cat│a│
+└────┴───┴─┘
+```
+
+Spot it? Between our two instances of `;: 'a tall cat'` we have two verbs: `\:` and `#&>`. Let's hook 'em.
+
+```
+   (\: #&>) ;: 'a tall cat'
+┌────┬───┬─┐
+│tall│cat│a│
+└────┴───┴─┘
+```
+
+Lastly, we can eliminate some whitespace and build our custom verb.
+
+```
+   sort =. \:#&>
+   sort ;: 'a tall cat'
+┌────┬───┬─┐
+│tall│cat│a│
+└────┴───┴─┘
+```
+
+## We did it!
+
+I hope this was a decently short and pleasant introduction into some fun features of the [J programming language](https://www.jsoftware.com/#/README):
+
+- [`& Bond`](https://www.jsoftware.com/docs/help804/dictionary/d630n.htm)
+- [`\: Sort Down`](https://www.jsoftware.com/docs/help804/dictionary/d432.htm)
+- [Hooks](https://www.jsoftware.com/docs/help804/primer/hook.htm)
+
+I encourage you to download J and play around with it. Hooks and forks and [other trains](https://www.jsoftware.com/docs/help804/dictionary/dictf.htm) pop up in all sorts of places and may make you think differently about the code you write everyday.
+
+Also consider [following me on twitter](https://twitter.com/jdan).
+
+Thanks for reading ✨