list_intersection

Calculate the intersection (list of common items) between two unformatted lists of char.

%let isec=%list_intersection(list1, list2, casense=no, unique=yes, sep=%quote( ));

Arguments

• list1, list2 : two lists of unformatted strings;
• casense : (option) boolean flag (yes/no) set to perform cases sensitive comparison/matching; default: casense=no, i.e. upper-case "intersection" items in both lists are matched;
• unique : (option) boolean flag (yes/no) set in combination with casense=no so as to return unique values from the input lists, independently of the case; in practice when unique=no, when two items present in the input lists with distinct (lower- and upper-) cases match through their upper-case versions (i.e., casense=no), both will be kept in the intersection list; default: unique=yes;
• sep : (option) character/string used as a separator in the input lists; default: sep=%quote( ), i.e. the input list1 and list2 are both blank-separated lists of items.

Returns

isec : output list of strings, namely the list of items obtained as the intersection list1 /\ list2, i.e. items common to both lists are preserved.

Examples

We first show some simple examples of use:

%let list1=A B C D E F A;
%let list2=C A B Z A;
%let isec1=%list_intersection(&list1, &list2);

returns: isec1=A B C, while:

%let isec2=%list_intersection(&list2, &list1);

returns a different: isec2=C A B. Then, also note the use of case sensitiveness:

%let list1=a B C D e F A;
%let list2=C A b Z A;
%let isec1=%list_intersection(&list1, &list2, casense=yes);

returns: isec1=C A. As for the use of the flag unique, note that:

%let isec2=%list_intersection(&list1, &list2);
%let isec3=%list_intersection(&list1, &list2, unique=no);

return: isec2=a B C and isec3=a B C A b respectively, while:

%let isec4=%list_intersection(&list2, &list1);
%let isec5=%list_intersection(&list2, &list1, unique=no);

return: isec4=C A b and isec5=C A b a B respectively.

Run macro %_example_list_difference for more examples.

Notes

1. As shown in the first example above, the order the lists are passed to the macro matters. Namely, the items, that are common to both lists list1 and list2, will be ordered in isec according to their order of appearance in the first list list1. For that reason, isec1 and isec2 above differ; still, it can be checked that:

%let res=%list_compare(&isec1,&isec2);

will return res=0, hence the sets supported by isec1 and isec2 are identical. Similarly, in the last example above:

%let res=%list_compare(&isec2,&isec4);

will return res=0 as well (only the order of the elements in the intersection lists differs).

1. Items present multiple times in input lists list1 and list2 are reported only once in the output intersection isec. For that reason, the item A in the first example above appears only once in isec1 and isec2. Items present multiple times with both lower- and upper-cases in the input lists will be reported only once in the output list iif unique=yes and casense=yes.
2. The parameter unique is ignored when casense=no.

See also

%list_difference, %list_compare, %list_append, %list_find, %list_unique, FINDW.