Utilities to filter data when using sqldf

[Gabor Grothendieck]

This stackoverflow post discusses some utilities that can usefully be used with the read.csv.sql and sqldf filter= arguments when reading variations of comma separated files into R.  This might be useful to some readers here.

https://stackoverflow.com/questions/52839580/notation-issues-with-read-csv-sql-in-r/52839896#52839896