The DAYOFWEEK function returns the day of week of the given date. The int value returned follows the ISO-8601 standard, from 1 (Monday) to 7 (Sunday).
dayofweek(format, date) : int
See DATE for a description of the date format.
The following example adds a column
x with the weekday number of the date in column
... | CALC x dayofweek('dd/MM/yyyy', first) | ...