How to check if there is any missing and replace - sas

Question

I have a dataset covering a number of companies for which there is a variable for the firms employees. Some years the number of employees has not been reported, hence a some years appear blank while the year before and after contains a value.
The data is similar to:
COMPANY YEAR NO. EMPLOYEES
Company 1 2007 4
Company 1 2008 5
Company 1 2009 5
Company 1 2010 5
Company 2 2007 11
Company 2 2008 10
Company 2 2009
Company 2 2010 10
Company 3 2007 3
Company 3 2008 4
Company 3 2009
Company 3 2010 3
I would like to be able to search the dataset for any such occurrences, making an indicator of these years, and afterwards replace any blank spots with the year before. If there is no previous year to use as a replacement or the previous year is blank, the year after the blank spot. I am hoping for the dataset to like:
COMPANY YEAR NO. EMPLOYEES
Company 1 2007 4
Company 1 2008 5
Company 1 2009 5
Company 1 2010 5
Company 2 2007 11
Company 2 2008 10
Company 2 2009 10
Company 2 2010 10
Company 3 2007 3
Company 3 2008 4
Company 3 2009 4
Company 3 2010 3
To sum up, at first i need to check whether or not i do have a problem with missing values in-between two years (important that the codes do not replace missing values before or after the last year with a non-missing value, since som firms exit the sample). Next, if any blank years in between any two years that are non-blank, I would like to replace these blank spots as mentioned above.

Answer 1

The method I would use:
1. Sort the dataset company/year.
2. Replace missing values using LAG function if the missing value is not the first observation of the company group.
3. Reverse the sort order
4. Repeat step 2 on the dataset with reversed order
5. Return the dataset to the original order
Please note, I have changed your original data for Company 3 in order to have a case for your second scenario (missing value, no previous record).
DATA HAVE;
input COMPANY $ 0-10 YEAR 13-17 N_EMPLOYEES 24-27;
datalines;
Company 1 2007 4
Company 1 2008 5
Company 1 2009 5
Company 1 2010 5
Company 2 2007 11
Company 2 2008 10
Company 2 2009
Company 2 2010 10
Company 3 2007
Company 3 2008 3
Company 3 2009 4
Company 3 2010 3
;
run;
PROC SORT DATA=HAVE
OUT=DOSOMEWORKHERE;
BY COMPANY YEAR;
RUN;
DATA DOSOMEWORKHERE (drop=PREV_N_EMPLOYEES);
set DOSOMEWORKHERE;
by COMPANY;
PREV_N_EMPLOYEES = LAG(N_EMPLOYEES);
if first.COMPANY then
do;
PREV_N_EMPLOYEES = .;
end;
if N_EMPLOYEES = . then N_EMPLOYEES = PREV_N_EMPLOYEES;
run;
PROC SORT DATA=DOSOMEWORKHERE
OUT=DOSOMEWORKHERE;
BY DESCENDING COMPANY DESCENDING YEAR ;
RUN;
DATA DOSOMEWORKHERE (drop=PREV_N_EMPLOYEES);
set DOSOMEWORKHERE;
by DESCENDING COMPANY;
PREV_N_EMPLOYEES = LAG(N_EMPLOYEES);
if first.COMPANY then
do;
PREV_N_EMPLOYEES = .;
end;
if N_EMPLOYEES = . then N_EMPLOYEES = PREV_N_EMPLOYEES;
run;
PROC SORT DATA=DOSOMEWORKHERE
OUT=WANT;
BY COMPANY YEAR;
RUN;
Result: