clist_permutation

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

%clist_permutation(par, _clist_=, seed=, mark=%str(%"), 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;
• mark, sep : (option) characters/strings used respectively as a "quote" and a separator in the input list; default: mark=str(%"), and" sep=%quote(,), i.e. the input clist is a comma-separated list of quote-enhanced items; see %clist_unquote for further details.

Returns

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

Examples

Using a fixed 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. If you need to use $, you can reset the global macro variable G_PING_UNLIKELY_CHAR (see _setup_ file) to another dumb (unlikely) character of your own.

See also

%ranuni, %list_sequence.