topic Re: How to use array for increment of lagX in SAS Programming

How to use array for increment of lagX

CheerfulChu — Mon, 17 Oct 2016 20:23:03 GMT

Dear Expert,

I have an array but it is not working. I have this WARNING: Apparent symbolic reference I not resolved. How do I write the following program

data XXX;
 
  array x {3) x1 - x3;
 
     x1 = act;
     x2 = lag1(act);
     x3 = lag2(act);
     x4 = lag3(act);
 
  end;
 
run;

into the program below

data XXX;

  array x {3) x1 - x3;

  do i = 1 to dim(x); 
     x{i} = lag&i.(act);
  end;

run;

Thank you so much

Re: How to use array for increment of lagX

Jim_G — Mon, 17 Oct 2016 20:42:21 GMT

Do you want 3 x values in each obs to reflect the last 3 values of act?

Data; set;

retain x1 x2 x3 0;

x3=x2;

x2=x1;

x1=act;

Jim

Re: How to use array for increment of lagX

CheerfulChu — Mon, 17 Oct 2016 20:54:03 GMT

Hi Jim and astounding,

Actually the number of lags I needed is 20. Also there is computational required for numerator and denominator

r1 = x1/a1;
...
r16 = x16 /a16;

where

x1 = act - ebb;
x2 = lag(act-ebb);
...
x16 = lag15(act -ebb);

a1 = alpha - beta;
...
a16 = lag15(alpha - beta);

alpha, beta, act, ebb are numbers.

I need it to write it in a data step because the modification I need to do is within a big data step.

another question:

lag(act - ebb) = lag(act) - lag(ebb) ?

I want to use the 2nd observations.

Re: How to use array for increment of lagX

Astounding — Mon, 17 Oct 2016 21:14:30 GMT

I can't sketch out the whole thing now, but you can extend the suggestion already made by using arrays. For example:

data want;

set have;

array x {16};

retain x1-x16;

do i=16 to 2 by -1;

x{i} = x{i-1};

end;

x1 = act - ebb;

run;

Similar computations need to be added for your other variables, but this is a workable approach.

Yes, you can apply LAG to computations not just to variable names.

Re: How to use array for increment of lagX

ballardw — Mon, 17 Oct 2016 21:14:44 GMT

Your error comes from:

x{i} = lag&i.(act);

&i represents a MACRO variable that you have not assigned.

To reference in an array you need to have a variable.

If you need to create a bunch of lagged variables you might try this brief macro:

%macro LagStem (basevar=,stem=, NumLags=);
   %do i = 1 %to &numLags;
    stem&i = lag&i(&basevar);
   %end;
%mend;

And use in your data step

data XXX;
  %LagStem(basevar=Act,stem=x,NumLags=15);
  array x {15) x1 - x15;
run;

It will be a very good Idea to call the macro immediately after any SET statement (since lag really doesn't mean much without a Set to read) and before use.

Note that it is up to you make sure to change the basevar and stem values so as not to overwrite your existing variables.

And Lag3 (x-y) isn't going to work. You will need to pull the lagged values in parallel and then calculate them in your data step.

Re: How to use array for increment of lagX

CheerfulChu — Mon, 17 Oct 2016 21:44:56 GMT

data test1; 
  set test; 
  array x {16} x1-x16;
  retain x1-x16; 
  do i = 16 to 2 by -1; 
    x{i} = {i-1}; 
  end; 
  x1 = atq - ibq; 
run;

I encountered this error

data test1; set test; array x {16} x1-x16;retain x1-x16; do i = 16 to 2 by
8 ! -1; x{i} = {i-1}; end; x1 = atq - ibq; run;
-
22
ERROR 22-322: Syntax error, expecting one of the following: a name, INPUT,
PUT.

ERROR: Undeclared array referenced: NAME.
ERROR: Variable NAME has not been declared as an array.
NOTE: The SAS System stopped processing this step because of errors.

Re: How to use array for increment of lagX

ballardw — Mon, 17 Oct 2016 22:13:20 GMT

Your error is referencing a variable that doesn't occur in your code. It is best to copy the code and error at one time from the log and then post using the "run" icon.

Re: How to use array for increment of lagX

Astounding — Mon, 17 Oct 2016 23:03:24 GMT

The actual code uses this formula:

x{i} = {i-1};

It should read:

x{i} = x{i-1};

Re: How to use array for increment of lagX

Ksharp — Tue, 18 Oct 2016 05:20:18 GMT

It is easy for IML.

proc iml;
use sashelp.class;
read all var {weight};
close;

lag=lag(weight,(0:4));
print lag;
quit;

OUTPUT:

lag
112.5	.	.	.	.
84	112.5	.	.	.
98	84	112.5	.	.
102.5	98	84	112.5	.
102.5	102.5	98	84	112.5
83	102.5	102.5	98	84
84.5	83	102.5	102.5	98
112.5	84.5	83	102.5	102.5
84	112.5	84.5	83	102.5
99.5	84	112.5	84.5	83
50.5	99.5	84	112.5	84.5
90	50.5	99.5	84	112.5
77	90	50.5	99.5	84
112	77	90	50.5	99.5
150	112	77	90	50.5
128	150	112	77	90
133	128	150	112	77
85	133	128	150	112
112	85	133	128	150