Quick Tip: Statistics on Booleans

Due to q’s type promotion rules, it’s entirely legal to use statistical functions on boolean vectors. avg tends to be the most useful, but all of them should work as expected.

A typical use case: average nullness (handy while developing ETL code). We will simulate with a vector of floats mistakenly parsed as ints (due to mostly looking like ints):

q)v:@[string 1000?1000;-10?1000;,[;".123"]]
q)t:flip(enlist`v)!(enlist"I";" ")0:v
q)t
v  
---
468
959
221
694
934
865
344
997
314
580
45 
745
898
935
64 
177
238
361
850
241
..
q)avg null t
v| 0.01
q)

So 10% of t.v is null, which (unless this is expected) should cause us to ask ourselves whether "I" was really the right parse.

What the Function?!?

q is notorious for its limited debugging features. One prominent aspect of this is the way runtime errors in the interactive shell are handled: you enter the debug shell and are presented with the body of the function that failed and the error that occurred. What’s missing? The name of the function!

So, to fill that gap, I’ve written a function wtf[] which will search the workspace for its argument, returning a fully-qualified name if it finds anything. wtf, along with brief documentation and a couple examples, can now be found in the lib subdirectory of my contrib (a section I hope to expand in the future).