Within a transducer stack modified by kv-ize, dynamically bound to the “current” key/index while being invoked with single/transduce-kv and multi/transduce-kv. Do not manually re-bind.

Concatenates vectors v1 and v2 eagerly and efficiently.

See benchmarking and analysis.

Examples:

(concatv) ;; => []
(concatv [11 22 33]) ;; => [11 22 33]
(concatv [11 22 33] [44 55 66]) ;; => [11 22 33 44 55 66]

Given a composition of transducing functions (a transducing stack) that only provides arities zero, one, and two, returns an equivalent transducer stack that also accepts result, key/index, and value, suitable for use with both transduce-kv variants, single/transduce-kv and multi/transduce-kv.

Intended for exploratory work or when the transducer stack is pre-composed. Otherwise, prefer composing transducer stacks with brokvolli.transducers-kv and brokvolli.stateful-transducers-kv.

The returned composition provides two additional capabilities.

1. Diverts the key/index provided by transduce-kv, passing only the accumulated value and the next element to the outer/top transducer, and
2. Establishes a binding context where the key/index is available by referencing *keydex* from any layer of the transducer stack.

Example, a transducer stack, out of our control:

(def xf-from-somewhere (comp (map inc)
                             (filter even?)
                             (take 3)))

(transduce-kv (kv-ize xf-from-somewhere) conj [11 22 33 44 55 66 77 88 99])
;; => [12 34 56]

Example, using clojure.core/filter instead of filter-kv, key/index accessible through dynamic var *keydex*:

(transduce-kv (kv-ize (filter (fn [_] (<= *keydex* 2)))) conj [11 22 33 44 55])
;; => [11 22 33]

An assoc variant, useful as the reducing function in a transduce operation.

• With no args, returns {}.
• With one arg, returns arg.
• With two args, associates y to *keydex* within x.
• With three args, associates y to z within x.

See also tconj for a similar utility used in transducing over sequential collections.

Example:

(transduce-kv (map-kv (fn [keydex x] {:keydex (inc keydex) :value x})) tassoc [11 22 33])
;; => {0 {:keydex 1, :value 11}
;;     1 {:keydex 2, :value 22}
;;     2 {:keydex 3, :value 33}}

A conj variant, useful as the reducing function in a transduce operation.

• With no args, returns [].
• With one arg, returns arg.
• With two args, conjoins y onto x.
• With three args, conjoins z onto x, ignoring the second arg (which is typically the key/index).

See also tassoc for a similar utility used in transducing over associative collections.

Example:

(transduce-kv (map-kv (fn [keydex x] [keydex x])) tconj [11 22 33])
;; => [[0 11] [1 22] [2 33]]