CODEWITHSUNDEEP
clojure
user14579348
user14579348

Reputation:

Remove nil in Clojure 2D-vector

What is the best way to remove the nils in a 2D-Vector in Clojure?

[[250 634]] [[450 598] [250 651]] [[450 615] [250 668]] [[450 632] [250 685]] [[450 649] [259 700]] [[450 666] [323 700]] [[450 683] [386 700]] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil]]

Upvotes: 0

Views: 408

Answers (3)

Thumbnail
Thumbnail

Reputation: 13473

mapv is a variant of map that returns a vector. In the same way, can define removev: a variant of remove that returns a vector:

(defn removev [pred v]
  (into [] (remove pred v)))

We can make a predicate that detects [nil nil] by wrapping it in a set: #{[nil nil]}.

By combining these, we have what we want:

(removev #{[nil nil]} [[1 3] [nil nil] [2 nil]])
=> [[1 3] [2 nil]]

I've just noticed that this answer is essentially the same as Denis Fuenzola's, except that this one converts the answer back to a vector.

Upvotes: 0

Denis Fuenzalida
Denis Fuenzalida

Reputation: 3346

You can use remove to remove elements out of a collection if they meet the criteria of a given predicate function. Now, you can use a set as a function, so you can use the set #{[nil nil]} to remove the undesired elements, like this:

user=> (def elems [[[250 634]] [[450 598] [250 651]] [[450 615] [250 668]] [[450 632] [250 685]] [[450 649] [259 700]] [[450 666] [323 700]] [[450 683] [386 700]] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil] [nil nil]])
#'user/elems

user=> (remove #{[nil nil]} elems)
([[250 634]] [[450 598] [250 651]] [[450 615] [250 668]] [[450 632] [250 685]] [[450 649] [259 700]] [[450 666] [323 700]] [[450 683] [386 700]])

Upvotes: 2

Jared Smith
Jared Smith

Reputation: 21926

(filter (fn [x] (every? not-nil x) your-vec)

Filters the vector by making sure that the sub-vector isn't just full of nils. If you want to filter out any vectors with nil use some instead of every?. If you want to keep the (potentially empty) sub-vectors then use filter instead of every?:

(filter (fn [x] (filter not-nil x) your-vec)

Upvotes: 0

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