Sorting data with Clojure #2
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| ## Getting started with (sort-by) | ||
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| The first requirement could be to sort a vector of invoices by total. These is relatively simple with `(sort-by)`: |
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I wouldn't refer to function names with parens around them -- (sort-by) -- unless you're showing a valid invocation. The naked sort-by is fine. Of course, this advice applies to all such instances in the article.
| (sort-by > :invoice/total-before-tax invoices) | ||
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| Now we’re cooking with gas! The most valuable invoices are now at the head of the list! Need the top 10? Just `(take 10)` and you’re set. |
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I would make the composition of sort-by and take explicit, with an example :-)
| This is where our friend `(juxt)` comes in. `(juxt)` accepts a list of functions and returns a new function, that when called, returns the results of all the original functions in a vector. | ||
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| ```clojure | ||
| (def head-and-tail (juxt [first last])) |
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juxt is variadic; it takes functions directly, rather than a single arg with a seq of functions:
https://clojuredocs.org/clojure.core/juxt
(juxt first last)
| (def negative-total (comp - :invoice/total-before-tax)) | ||
| (negative-total invoice) #=> -100 | ||
| ``` | ||
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If this right-to-leftness of comp bothers you, you could also simply declare it as an anonymous function which wraps a thread-first functional pipeline: #(-> % :invoice/total-before-tax -).
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Thanks @robert-stuttaford for the great feedback! I'm thinking of just dropping the section on unsortables, or is there something important worth mentioning? The only things I could think off is infinite streams can't be sorted and lazy sequences are forced to be evaluated... |
Would love some feedback here or via Slack 🙏
/cc @robert-stuttaford @vmpj @alndvz