(join xrel yrel)
(join xrel yrel km)
When passed 2 rels, returns the rel corresponding to the natural
join. When passed an additional keymap, joins on the corresponding
keys.
Source
(defn join
"When passed 2 rels, returns the rel corresponding to the natural
join. When passed an additional keymap, joins on the corresponding
keys."
{:added "1.0"}
([xrel yrel] ;natural join
(if (and (seq xrel) (seq yrel))
(let [ks (intersection (set (keys (first xrel))) (set (keys (first yrel))))
[r s] (if (<= (count xrel) (count yrel))
[xrel yrel]
[yrel xrel])
idx (index r ks)]
(reduce (fn [ret x]
(let [found (idx (select-keys x ks))]
(if found
(reduce #(conj %1 (merge %2 x)) ret found)
ret)))
#{} s))
#{}))
([xrel yrel km] ;arbitrary key mapping
(let [[r s k] (if (<= (count xrel) (count yrel))
[xrel yrel (map-invert km)]
[yrel xrel km])
idx (index r (vals k))]
(reduce (fn [ret x]
(let [found (idx (rename-keys (select-keys x (keys k)) k))]
(if found
(reduce #(conj %1 (merge %2 x)) ret found)
ret)))
#{} s))))