Hi, After reviewing all the other alternatives like SQL and Python UDF, I was either stuck on performance with SQL UDF or on usability with Python UDF (unable to use with aggregation, and not such great performance with dates), so I decided to go the hard way with C functions, as a bonus it will give me the possibility to change the functionalities without worrying about dependencies, which was not the case in other languages. The purpose is to create a set of formatting functions for Year, Quarter, Month, Week and Day brackets, and of course i need to create the bulk version of each function for performance. Starting from the MTIMEdate_extract_year_bulk, now i have the simple function working, and successfully calling it from mclient: *str* *UDFyearbracket(str *ret, const date *v)* *{* * if (*v == date_nil) {* * *ret = GDKstrdup(str_nil);* * } else {* * int year;* * fromdate(*v, NULL, NULL, &year);* * *ret = (str) GDKmalloc(15);* * sprintf(*ret, "%d", year);* * }* * return MAL_SUCCEED;* *}* For the bulk version i get an error in the log: gdk_atoms.c:1345: strPut: Assertion `(v[i] & 0x80) == 0' failed. *str* *UDFBATyearbracket(bat *ret, const bat *bid)* *{* * BAT *b, *bn;* * BUN i,n;* * str *y;* * const date *t;* * if ((b = BATdescriptor(*bid)) == NULL)* * throw(MAL, "UDF.BATyearbracket", "Cannot access descriptor");* * n = BATcount(b);* * bn = COLnew(b->hseqbase, TYPE_str, BATcount(b), TRANSIENT);* * if (bn == NULL) {* * BBPunfix(b->batCacheid);* * throw(MAL, "UDF.BATyearbracket", "memory allocation failure");* * }* * bn->tnonil = 1;* * bn->tnil = 0;* * t = (const date *) Tloc(b, 0);* * y = (str *) Tloc(bn, 0);* * for (i = 0; i < n; i++) {* * if (*t == date_nil) {* * *y = GDKstrdup(str_nil);* * } else* * UDFyearbracket(y, t);* * if (strcmp(*y, str_nil) == 0) {* * bn->tnonil = 0;* * bn->tnil = 1;* * }* * y++;* * t++;* * }* * BATsetcount(bn, (BUN) (y - (str *) Tloc(bn, 0)));* * bn->tsorted = BATcount(bn)<2;* * bn->trevsorted = BATcount(bn)<2;* * BBPkeepref(*ret = bn->batCacheid);* * BBPunfix(b->batCacheid);* * return MAL_SUCCEED;* *}* PS: I am not a c expert but i can find my way with basic operations and pointers. Any help or suggestions is appreciated. Thank you.