# Neighbours in Matrix (in Clojure)

Code snip of how to find neighbours in a matrix:

```
(ns core)
(defn build-matrix
[rows cols]
(mapv (fn [row]
(vec (range (+ 1 (* row cols))
(+ (* (+ row 1) cols) 1))))
(range 0 rows)))
(defn build-square-matrix
[size]
(build-matrix size size))
(defn neighbours
([matrix start-pos]
(neighbours [[-1 0] [+1 0] [0 1] [0 -1]] matrix start-pos))
([neighbouring matrix start-pos]
(let [neighbour-positions (map #(mapv + start-pos %) neighbouring)]
(filterv #(get-in matrix %) neighbour-positions))))
(defn neighbours-vals
"Access values in a matrix by xy position, starting at [0,0]"
[matrix start-pos]
(mapv #(get-in matrix %) (neighbours matrix start-pos)))
(comment
(def matrix (build-square-matrix 10))
(neighbours matrix [1 1])
(get-in matrix [1 1])
(neighbours-vals matrix [1 1])
(get-in matrix [4 4])
(neighbours-vals matrix [4 4])
;;
)
```

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