Happy New Year all!
I am working on a permutation test but I am stuck on obtaining all the possible permutations. I am using proc iml and what I want to do is to obtain individual data sets for each possible swapping of two rows in a matrix. I supplied a sample data set and the code I am using below. Currently, this proc iml SAS code is rearranging multiple rows so the first problem is to adjust it so only two rows are swapped at a time. The second problem is to repeat the procedure for every possible unique row permutation (without resampling). For example, this data set would have 10 different "b" data sets produced for the 10 possible ways two rows can be swapped. Let me know if further explanation is needed. I am open to other methods but so far I have found proc iml to be the most useful. Thanks!!
data ys;
do i = 1 to 10;
call streaminit(123);
u1 = rand("Uniform");
y_12 = ceil(5*u1);
call streaminit(456);
u2 = rand("Uniform");
y_13 = ceil(5*u2);
call streaminit(789);
u3 = rand("Uniform");
y_23 = ceil(5*u3);
output;
end;
drop u1 u2 u3 i;
run;
/* permutation test */
/*this works but it currently swaps more than two rows. I need to edit so only two rows are swapped at a time = single permutation*/
/*Source: http://blogs.sas.com/content/iml/2010/10/06/generating-random-permutations/*/
proc iml;
/** generate one random permutation with N>0 elements **/
start RandPerm(N);
u = 1:N; /** allocate u **/
call randgen(u, "Uniform"); /** fill with random numbers **/
return(rank(u)); /** return rank (order) of elements **/
finish;
/** call the permutation module **/
call randseed(123); /** optional: make numbers reproducible **/
p = RandPerm(10);
print p;
/** Module to permute the rows of a matrix **/
start PermuteRows(M);
n = nrow(M); /** how many rows? **/
r = RandPerm(n); /** get a random permutation **/
return ( M[r,] ); /** return matrix with permuted rows **/
finish;
/** test the module **/
use ys;
read all var {y_12 y_13 y_23} into a;
b = PermuteRows(a);
print a;
print b;
Here is the current output:
a
3 1 1
2 2 2
2 1 1
1 5 2
3 5 4
5 2 5
1 3 5
1 1 1
4 4 5
4 3 5
b
4 4 5
2 2 2
3 5 4
4 3 5
5 2 5
1 1 1
2 1 1
1 3 5
3 1 1
1 5 2
Here is an example of the desired output (notice only two rows are swapped here: row 3 & row 9). Then, the next step is to repeat the procedure to create data sets for each possible row exchange.
a
3 1 1
2 2 2
2 1 1
1 5 2
3 5 4
5 2 5
1 3 5
1 1 1
4 4 5
4 3 5
b
3 1 1
2 2 2
4 4 5
1 5 2
3 5 4
5 2 5
1 3 5
1 1 1
2 1 1
4 3 5
