Look up to upper value

[harrylui]

good day all,

here is  my data set

Obs	Date	rownum
1	01APR2021	1
2	.	2
3	02APR2021	3
4	05APR2021	4
5	06APR2021	5
6	07APR2021	6
7	.	7
8	08APR2021	8
9	09APR2021	9
10	12APR2021	10
11	.	11
12	13APR2021	12
13	14APR2021	13
14	15APR2021	14
15	16APR2021	15
16	19APR2021	16
17	20APR2021	17
18	21APR2021	18
19	22APR2021	19
20	23APR2021	20
21	26APR2021	21
22	27APR2021	22
23	28APR2021	23
24	29APR2021	24
25	30APR2021	25

for the missing value, i want to write a program for auto look up the upper value.

for the example Obs 2 will equal 01APR2021. i know a function called retain would do . But can i use if then for my question?  if date is missing , then date =  date (current rownum-1).  if it is possible, i can be more creative in my future program. thanks you

Regards,

Harry

[mkeintz · Accepted solution]

Here is a way to use an IF test, via the IFN function:

data want;
  set have;
  date=ifn(date=.,lag(date),date);
run;

But this only replaces all missing date values when there are never two consecutive missing date values.

A more general solution:

data want (drop=_:);
  set have (rename=(date=_check));
  if _check ^=. then set have point=_n_;
run;

This relies on the fact that variables read via a SET statement are automatically retained - until another SET reads in the same variable, which usually happens with every incoming obs.  But the conditional set statement above (if _check^=. then set have point=_n_) only reads non-missing values for DATE and automatically retains that value.  And unlike the first example, this would propagate non-missing DATE values over multiple consecutive observations with missing values for _CHECK.

[harrylui]

thank you so much