slope1.d

void init(T, U, V)(ref T[U] assoc, U where, lazy V how) {  static assert(is(V: T));  if (!(where in assoc)) assoc[where]=how;}struct slope1(I, U) { /// Items and Users  struct userPrefs { U user; float[I] ratings; }  float[I][I] diffs;  size_t[I][I] freqs;  void update(userPrefs[] prefs) {    foreach (entry; prefs) foreach (item, rating; entry.ratings) {      init(diffs, item, (float[I]).init);      init(freqs, item, (size_t[I]).init);      foreach (item2, rating2; entry.ratings) {        init(diffs[item], item2, 0f);        init(freqs[item], item2, 0);        freqs[item][item2]+=1;        diffs[item][item2]+=rating-rating2;      }    }    foreach (item, ratings; diffs)      foreach (item2, rating; ratings)        ratings[item2]/=freqs[item][item2];  }  float[I] predict(userPrefs prefs) {    float[I] preds; size_t[I] freqs;    foreach (item, rating; prefs.ratings) {      foreach (diffitem, diffratings; diffs) {        if (!(diffitem in this.freqs) || (!(item in this.freqs[diffitem]))) continue;        auto freq=this.freqs[diffitem][item];        init(preds, diffitem, 0f);        init(freqs, diffitem, 0);        preds[diffitem]+=freq*(diffratings[item] + rating);        freqs[diffitem]+=freq;      }    }    float[I] res;    foreach (item, value; preds) if (!(item in prefs.ratings) && freqs[item]>0) res[item]=value/freqs[item];    return res;  }}template constEnum(T, int start, S...) {  static if(S.length)    const char[] constEnum="const "~T.stringof~" "~S[0]~" = "~start.stringof~"; "~constEnum!(T, start+1, S[1..$]);  else const char[] constEnum="";}import std.stdio;void main() {  typedef int critters;  mixin(constEnum!(critters, 0, "cuttlefish", "octupus", "squid", "nautilus"));  typedef slope1!(critters, string) mySlope;  mySlope s;  s.update([    mySlope.userPrefs("alice", [squid: 1f, cuttlefish: .5f, octupus: .2f]),    mySlope.userPrefs("bob", [squid: 1f, octupus: 0.5f, nautilus: 0.2f]),    mySlope.userPrefs("carole", [squid: .2f, octupus: 1f, cuttlefish: .4f, nautilus: .4f]),    mySlope.userPrefs("dave", [cuttlefish: 0.9f, octupus: 0.4f, nautilus: 0.5f])  ]);  writefln(s.predict(mySlope.userPrefs("", [squid: 0.4])));}xt4100 ~/d $ gdc slope1.d -o slope1 && ./slope1[0:0.25,1:0.233333,3:0.1]