list_permutation

Perform a pseudo-random permutation of either the elements of a list or a sequence of integers.

%list_permutation(par, _list_=, seed=0, sep=%quote( ));

Arguments

• par : input parameter; this can be:
  • either a positive INTEGER defining the desired length of the output list,
  • or a list whose items will be permuted/shuffled;
• seed : (option) seed of the pseudo-random numbers generator; if seed<=0, the time of day is used to initialize the seed stream; default: seed=0; see %ranuni;
• sep : (option) character/string separator in input list; default: %quote( ), i.e. sep is blank.

Returns

_list_ : output sequenced list, i.e. the length of the considered list (calculated as the number of strings separated by sep).

Examples

Using a fixed >0 seed, it is possible to retrieve pseudo-random lists (sequence) of INTEGER values, e.g.:

%let olist=;
%let seed=1;
%let par=10;
%list_permutation(&par, _list_=olist, seed=&seed);

(always) returns olist=9 10 1 4 3 8 7 5 6 2, while using the same seed over some lists of NUMERIC or CHAR lists enables us to permute the items of the lists, e.g.:

%let par=a b c d e f g h i j;
%list_permutation(&par, _list_=olist, seed=&seed);
%let alist=;
%let par=-2 105 43 56 89 0.5 8.2 10 1 0;
%list_permutation(&par, _list_=alist, seed=&seed);

return always the same lists olist=i j a d c h g e f b and alist=1 0 -2 56 43 10 8.2 89 0.5 105.

Run macro %_example_list_permutation for examples.

Notes

1. In the example above, one can simply check that %list_compare(&par, &olist)=0 holds.
2. The macro will not return exactly what you want if the symbol £ appears somewhere in the list.

See also

%ranuni, %list_sequence, %list_sort.