topic Saving vectors into a matrix in SAS/IML Software and Matrix Computations

Saving vectors into a matrix

Tzachi — Wed, 09 Sep 2015 11:55:43 GMT

I have a set of vectors that i generate by randomly sampling from a larger vector (the item are words/characters).
I do it in a do loop and after each iteration i have a 1*4 or a 1*3 vector. I would like to collect all of these vectors into a matrix whose size is N*4, where N is the number of loops. In cases where the vectors are 1*3, the last item in a row of a matrix will be missing. I was hoping to initially create a N*4 matrix of zeros, and after each loop, insert the vector (either the 1*3 or 1*4) in row i, where i go from 1 to N.

Can anyone suggest an efficient code for implementing this task?

Thanks for your help,

Tzachi

Re: Saving vectors into a matrix

Rick_SAS — Wed, 09 Sep 2015 12:31:29 GMT

It would have been useful for you to have posted your code.

Because you are storing character values, you can't allocate a numerical matrix of zeros. Instead you need to allocate a character matrix of blank strings. See the article "How to create a string of a specified length" for tips about how to create a matrix that contains a matrix that contains all blank strings. Then inside the loop you look at the number of elements of each sample and assign it to columns 1:3 or 1:4 of the i_th row, as follows:

proc iml;
call randseed(1234);
list = {peter piper picked a peck of pickled peppers};
N = 10;

/* determine number of items */
numItems = sample({3 4}, N);
print numItems;

/* Allocate matrix for results. See 
   http://blogs.sas.com/content/iml/2014/05/12/how-to-create-a-string-of-a-specified-length-in-sasiml.html */
results = j(N, 4, BlankStr(nleng(list)));
do i = 1 to N;
   items = sample(list, numItems[i]);
   results[i, 1:ncol(items)] = items;
end;
print results;

Re: Saving vectors into a matrix

Tzachi — Thu, 10 Sep 2015 21:32:30 GMT

Thanks very much Rick!