Picking Out Elements Using a Logical List

[Eddie W. Shore]

I am taking an online class in R Programming language (http://www.edx.org), having a great time. The program BOOLLIST is based on the ability in R to pick out elements using logical elements (TRUE, FALSE).


Example (in R):

vector <- [2, 3, 4, 5]
vector[ c(TRUE, TRUE, FALSE, TRUE) ] returns [2, 3, 5]

The logical vector doesn’t have to be same length as the source vector. If the logical vector has elements than the source vector.

vector <- [1, 2, 3, 4, 5, 6]
vector[ c(TRUE, FALSE, TRUE, FALSE, TRUE, FALSE) ] returns [1, 3, 5]
vector[ c(TRUE, FALSE) ] returns [1, 3, 5] (TRUE, FALSE pattern recycles)

Program BOOLLIST:

Input: BOOLLIST(source list, logical list)

Notes: Use list brackets { }. For the logical list, use 1 for TRUE and 0 for FALSE.

Code:

EXPORT BOOLLIST(LA, LB)
BEGIN

LOCAL LC, n, s, k, j;

//  Initialization
LC≔{ };
j≔1;
s≔SIZE(LA);
b≔SIZE(LB);

// Process
FOR k FROM 1 TO s DO
 
IF LB(j)==1 THEN
LC≔CONCAT(LC,LA(k));
END;

j≔j+1;

IF j>n THEN
j≔1;
END;

END;

RETURN LC;

END;

Examples:

In addition to the examples above that can be tried with BOOLLIST:

BOOLLIST( {4,2,3,6}, {1,0,0,1} ) returns {4, 6}

BOOLLIST( {3,9,6,-1,6}, {1,0} ) returns {3, 6, 6}

http://edspi31415.blogspot.com/2015/08/h...using.html