CODEWITHSUNDEEP
clojure
Roland
Roland

Reputation: 5438

How to handle lists when assoc-in/get-in etc

I started with a csv-file. I have slurped it and added some structure with partition-by and sorted with sort-by. But now I'd like to add values to keep track of processing. But get-in and assoc-in don't like lists. And although I haven't added lists the partition-by seems to like them.

So, how to get out of this situation? Is there a way to transform all lists inside a structure to vectors or an alternative version of partition-by that isn't such a crybaby about lists or do I need to rethink my solution somehow? :-)

A simple example of a structure

(sort '(1 2 3 4 5))

Upvotes: 1

Views: 156

Answers (2)

Chris Murphy
Chris Murphy

Reputation: 6509

If your structure is a list of lists called xs, then you can:

(mapv vec xs)

That will give you a vector of vectors. A vector is an associative data structure (unlike a list), so get-in and assoc-in will work. However if there are more meaningful keys than the position of an element in a vector, then you might prefer to work with maps, in which case you would have a collection (vector or list) of homogeneous maps, which is a common way of working with data.

And just for verification:

(mapv vec '((1 2 3) (4 5 6)))
;;=> [[1 2 3] [4 5 6]]

Upvotes: 0

Magos
Magos

Reputation: 3014

If you want to transform the lists and then use the associative interface, clojure.walk has utilities that allow you to do that transformation on arbitrarily nested structures. 

(let[my-nested-structure {:foo '(1 2 4) '(0) :bar :baz {42 '()}}]
  (clojure.walk/postwalk #(if (list? %) (vec %) %) my-nested-structure))
;; => {:foo [1 2 4], [0] :bar, :baz {42 []}}

postwalk and prewalk are effectively the same in this instance but the difference can matter if your replacement function adds/removes sub-entries.

The specter library might also interest you - its transform, select and so on allow you to approach get-in type jobs from a slightly different direction and with that data structure agnosticism.

Upvotes: 1

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