http://rosettacode.org/wiki/Merge_and_aggregate_datasets
After looking at this rosettacode task, I decided that Jd is probably best suited for the J task implementation. So, I am not trying to learn Jd (I had not had occasion to use it, previously). After a few minor mishaps, I've stumbled on an issue which I do not know how to resolve. (Previous mishaps: csvload fails with an error suggesting that the file does not exist if csvprepare has not been previously run. This behavior is undocumented, except by example in the tutorials. Also, I need to run the tutorial in a different J session from my testing work to prevent the tutorials from breaking my tests.) Anyways, I'm currently getting an Unrecognized aggregate function error, when trying to use the 'max' aggregate function. This should demonstrate where I'm at: require'jd pacman' load JDP,'tools/csv_load.ijs' F=: jpath '~temp/rosettacode/example/CSV' jdcreatefolder_jd_ CSVFOLDER=: F assert 0<{{)n PATIENTID,LASTNAME 1001,Hopper 4004,Wirth 3003,Kemeny 2002,Gosling 5005,Kurtz }} fwrite F,'patients.csv' assert 0<{{)n PATIENTID,VISIT_DATE,SCORE 2002,2020-09-10,6.8 1001,2020-09-17,5.5 4004,2020-09-24,8.4 2002,2020-10-08, 1001,,6.6 3003,2020-11-12, 4004,2020-11-05,7.0 1001,2020-11-19,5.3 }} fwrite F,'visits.csv' csvprepare 'patients';F,'patients.csv' csvprepare 'visits';F,'visits.csv' csvload 'patients';1 csvload 'visits';1 jd'ref patients PATIENTID visits PATIENTID' echo jd ([echo) deb {{)n reads p.PATIENTID, LASTNAME:p.LASTNAME, first v.VISIT_DATE by p.PATIENTID from p:patients, v:p.visits }} -.LF Now, ... one of my thoughts was that maybe this is a type error, indicating that 'max' does not have a definition for the type of data in this column. However, replacing 'max' with 'first' (which should be defined for any type of column) also gives an "Unrecognized aggregate function' error. So... (1) What am I doing wrong here, and (2) What should I have looked at to discover this information? Thanks, -- Raul ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm