Assign value flag based on condition

[Q1983]

data have;

input DOW $ HOLIDAY_FLG $ DATE DATE9.;

FORMAT DATE DATE9.;

DATALINES;

MON Y 1JAN2018

TUE N 2JAN2018

WED N 3JAN2018

THU N 4JAN2018

FRI N 5JAN2018

SAT N 6JAN2018

notice that 1jan2018 is a holiday.  If I encounter a holiday on a Monday I want to add a field called date_flg and say

MON Y 1JAN2018    4

TUE N 2JAN2018     2

WED N 3JAN2018    2

THU N 4JAN2018     2

FRI N 5JAN2018      2

;

RUN;

If Mon is a holiday I want the date_flg to equal 4, the remaining days of the week should equal 2

If Mon is NOT a holiday I want the date_flg to equal 3 and the remaining days of the week should equal 1 

I tried the lag function without success.  Essentially I am attempting to evaluate previous row and populate based on this.  Any ideas

[ChrisNZ]

Like this?

data WANT;
  retain MON_IS_HOL;
  set HAVE;
  if DOW = 'MON' then MON_IS_HOL=(HOLIDAY_FLG='Y');
  if DOW = 'MON' then DATE_FLG=3+MON_IS_HOL;
  else                DATE_FLG=1+MON_IS_HOL;
run;

DOW	HOLIDAY_FLG	DATE	DATE_FLG
MON	Y	01JAN2018	4
TUE	N	02JAN2018	2
WED	N	03JAN2018	2
THU	N	04JAN2018	2
FRI	N	05JAN2018	2
SAT	N	06JAN2018	2