why.clj

(defn sparse-vector
  "Takes in a sequence of 2-tuples of the form `<idx, val>` and
  generates a sparse vector with each `val` inserted at its
  corresponding `idx`. Missing values will be set to the supplied
  placeholder."
  ([size placeholder tuples]
     (sparse-vector 0 size placeholder tuples))
  ([offset size placeholder tuples]
     (loop [idx 0
            tup-seq tuples
            v (transient [])]
       (let [[pos val] (first tup-seq)]
         (cond (>= idx size) (persistent! v)
               (= idx pos) (recur (inc idx) (rest tup-seq) (conj! v val))
               :else       (recur (inc idx) tup-seq (conj! v placeholder)))))))

(sparse-vector 0 10 0 [[4 1]])
;=> [0 0 0 0 1 0 0 0 0 0]

(defn sparse-vector
  "Takes in a sequence of 2-tuples of the form `<idx, val>` and
  generates a sparse vector with each `val` inserted at its
  corresponding `idx`. Missing values will be set to the supplied
  placeholder."
  ([size placeholder tuples]
     (sparse-vector 0 size placeholder tuples))
  ([offset size placeholder tuples]
     (loop [idx 0
            tup-seq tuples
            v (transient [])]
       (let [[pos val] (first tup-seq)
             p (- pos offset)]
         (cond (>= idx size) (persistent! v)
               (= idx pos) (recur (inc idx) (rest tup-seq) (conj! v val))
               :else       (recur (inc idx) tup-seq (conj! v placeholder)))))))

(sparse-vector 0 10 0 [[4 1]])

No message.
  [Thrown class java.lang.NullPointerException]

Restarts:
 0: [QUIT] Quit to the SLIME top level

Backtrace:
  0: clojure.lang.Numbers.ops(Numbers.java:1364)
  1: clojure.lang.Numbers.minus(Numbers.java:128)
  2: forma.matrix.utils$sparse_vector.invoke(NO_SOURCE_FILE:1)
  3: forma.matrix.utils$eval7239.invoke(NO_SOURCE_FILE:1)
  4: clojure.lang.Compiler.eval(Compiler.java:5424)
  5: clojure.lang.Compiler.eval(Compiler.java:5391)
  6: clojure.core$eval.invoke(core.clj:2382)
  7: swank.core$eval922$fn__923.invoke(core.clj:409)
  8: clojure.lang.MultiFn.invoke(MultiFn.java:163)
  9: swank.commands.basic$eval_region.invoke(basic.clj:48)
 10: swank.commands.basic$eval_region.invoke(basic.clj:38)
 11: swank.commands.basic$eval1223$listener_eval__1224.invoke(basic.clj:72)
 12: clojure.lang.Var.invoke(Var.java:365)
 13: forma.matrix.utils$eval7237.invoke(NO_SOURCE_FILE)
 14: clojure.lang.Compiler.eval(Compiler.java:5424)
 15: clojure.lang.Compiler.eval(Compiler.java:5391)
 16: clojure.core$eval.invoke(core.clj:2382)
 17: swank.core$eval_in_emacs_package.invoke(core.clj:94)
 18: swank.core$eval_for_emacs.invoke(core.clj:241)
 19: clojure.lang.Var.invoke(Var.java:373)
 20: clojure.lang.AFn.applyToHelper(AFn.java:169)
 21: clojure.lang.Var.applyTo(Var.java:482)
 22: clojure.core$apply.invoke(core.clj:540)
 23: swank.core$eval_from_control.invoke(core.clj:101)
 24: swank.core$eval_loop.invoke(core.clj:106)
 25: swank.core$spawn_repl_thread$fn__881$fn__882.invoke(core.clj:320)
 26: clojure.lang.AFn.applyToHelper(AFn.java:159)
 27: clojure.lang.AFn.applyTo(AFn.java:151)
 28: clojure.core$apply.invoke(core.clj:540)
 29: swank.core$spawn_repl_thread$fn__881.doInvoke(core.clj:317)
 30: clojure.lang.RestFn.invoke(RestFn.java:398)
 31: clojure.lang.AFn.run(AFn.java:24)
 32: java.lang.Thread.run(Thread.java:680)