calculate the macro variable in sas macro

[ffgsdf]

hi every one,

I am try to write a k-means algorithm in one dimension data in sas macro. 

First step, I trying to randomly sample three object from 1 to 13 and name them as k1, k2, and k3.

second step, I want to calculate each the difference between my variable and k1 to t3 to decide which one belongs to which cluster.

However, i cannot calcuate the macro variable in sas. 

the following is my code. 

data t;

INPUT x;
cards;
1
2
3
4
5
6
7
8
9
10
11
12
13
;
%macro a(data,k,var);
proc surveyselect data=&data noprint
METHOD=srs
SEED=0
OUT=t1
SAMPSIZE=&k;
RUN;
data t1;
set t1;
n=_N_;
run;
%do i = 1 %to &k;
proc sql noprint;select x INTO :k&i from t1 where n=&i;
data t;
set t;
y&i=x-k&i;
run;
%end;
%mend a;
%a(data=t,k=3,var=x);

I found that I have successfully create the three sas macro variable k1 to k3 and test them using 

%put &k1.

However, how could I write the calcuation in sas macro. 

there is a problem in "y&i=x-k&i;".

sas cannot read k&i as macro variable. 

how could I resovle this?

thx
 

[FreelanceReinh · Accepted solution]

Hi @ffgsdf,

Please change the definition of the "y&i" to:

y&i=x-&&k&i;

Edit:

Explanation: Without the double ampersand k&i resolves to k1 in the first iteration of the %DO loop, to k2 in the second and to k3 in the third. Thus, you are seemingly referring to data step variables k1, k2, k3, which previously did not exist (log messages: "NOTE: Variable k1 is uninitialized." and "NOTE: Missing values were generated ..."). However, you want to refer to your macro variables k1, k2, k3.

With the corrected code, the macro processor resolves "&&" to "&" and "&i" to 1 (in the first iteration of the %DO loop) in the first pass, and then, in the second pass, &k1 to the value of macro variable k1, as desired.