— Function: LAG (variable[, ncases])

variable must be a numeric or string variable name. LAG results in the value of that variable for the case ncases before the current one. In case-selection procedures, LAG results in the value of the variable for the last case selected. Results in system-missing (for numeric variables) or blanks (for string variables) for the first case or before any cases are selected.

If omitted, ncases defaults to 1. Otherwise, ncases must be a small positive constant integer. There is no explicit limit, but use of a large value will increase memory consumption.

— Function: YRMODA (year, month, day)

year is a year, either between 0 and 99 or at least 1582. Unlike other PSPP date functions, years between 0 and 99 always correspond to 1900 through 1999. month is a month between 1 and 13. day is a day between 0 and 31. A day of 0 refers to the last day of the previous month, and a month of 13 refers to the first month of the next year. year must be in range. year, month, and day must all be integers.

YRMODA results in the number of days between 15 Oct 1582 and the date specified, plus one. The date passed to YRMODA must be on or after 15 Oct 1582. 15 Oct 1582 has a value of 1.