topic Re: Creating New Values Based on Last Observation's Number and current observation's percent in SAS Programming

Creating New Values Based on Last Observation's Number and current observation's percent

KellyMcAllister — Wed, 26 Apr 2017 20:20:26 GMT

I am looking to populate a variable that has missing numbers for future years (say 2018 through 2030). What I have is a population number for 2017, and I have given growth percents for the future years. So, for 2018, I want to take the population value (say 800) from the last observation for year 2017 and multiply that by my growth percent that I have stored in the observation for 2018. I tried using a retain statement, and I was able to get this to work for the first year, but I am unable to get it to carry over for the remaining years.

My data structure is as follows:

year	population	growth_percent

2017	800	1.01
2018	x1	1.06
2019	x2	1.08
2020	x3	1.11
2021	x4	1.5
2022	x5	1

I need to dynamically calculate the numbers for x1 - x5.

X1 should equal 800 * 1.06. Then X2 should eqaul X1 * 1.08.

I have tried the following code, but I am only able to populate X1. I can't figure out how to pass the X1 value to the next observation in order to calculate X2:

data populations;

set pop;

retain lastpop;

output;

lastpop= (population) * (growth_percent);

run;

Much Thanks!

Re: Creating New Values Based on Last Observation's Number and current observation's percent

thomp7050 — Wed, 26 Apr 2017 20:32:54 GMT

Kelly,

I recommend that you try to get that original number out of the x1, x2 etc. column. From there, you can multiply it against the growth percentage.

Assuming that it is always the least year that gives you the original population, you can do the following:

data have;  
input year population $ growth_percent  ;
FORMAT growth_percent 8.4;
cards;  
2017	800	1.01
2018	x1	1.06
2019	x2	1.08
2020	x3	1.11
2021	x4	1.5
2022	x5	1
;
run;

PROC SQL;
CREATE TABLE MIN AS 
SELECT INPUT(POPULATION, 8.) AS MIN_POP FORMAT=8. FROM HAVE WHERE YEAR IN (SELECT MIN(YEAR) FROM HAVE);
QUIT;

PROC SQL;
CREATE TABLE HAVE AS 
SELECT *, MIN.MIN_POP * GROWTH_PERCENT AS TOTAL_GROWTH FROM HAVE, MIN;
QUIT;

There are many other ways to do this I am sure, but I prefer SQL because it may be used in many other statistical programs (e.g. R, SPSS, etc.)

Re: Creating New Values Based on Last Observation's Number and current observation's percent

KellyMcAllister — Wed, 26 Apr 2017 20:50:03 GMT

I need to be able to pass the TOTAL_GROWTH # to the next observation:

2017: 800 * 1.01 = 808

2018: 808 * 1.06 = 856.48 (****not: 800 *1.06 = 848)

2019: 856.48 * 1.08 = 924.9984

and so on...

Re: Creating New Values Based on Last Observation's Number and current observation's percent

Astounding — Wed, 26 Apr 2017 20:55:50 GMT

Assuming your data is in order, a simple program would be:

data want;

set have;

retain new_pop;

if year = 2017 then new_pop = population;

else new_pop = new_pop * growth_percent;

drop population;

rename new_pop = population;

run;

Re: Creating New Values Based on Last Observation's Number and current observation's percent

KellyMcAllister — Wed, 26 Apr 2017 21:05:13 GMT

Thank you so much! This is exactly what I needed.

Re: Creating New Values Based on Last Observation's Number and current observation's percent

mkeintz — Wed, 26 Apr 2017 21:05:25 GMT

data want2 (drop=lastpop);
  set have;
  if pop=. then pop=lastpop*gr_pct;
  retain lastpop;
  lastpop=pop;
run;

This program assumes that the first observation always has a proper value for population. Also, anytime a new value for population is encountered in the input data step, the process start over.