The relational
operators >, >=, <, <=,
and == return a logical result, a scalar,
series, or array whose elements are either 1 (true) or
0 (false).
a = 1..10;
b = a > 5;
The expression
a > 5 produces the logical series:
b == {0, 0, 0, 0, 0, 1, 1, 1, 1, 1}
A logical series can be used directly to index another series:
c = a[b]
Result:
c == {6, 7, 8, 9, 10}
Wherever b
is 1, the corresponding
element of a is selected; wherever b is 0, the element is ignored.
This is equivalent to:
c = a[a > 5]
and also to:
c = a[find(a > 5)]
The LOGICAL function will convert a series to a logical series by setting the output element to 1 where the input element is nonzero and setting the output element to 0 wherever the input element is 0.
The ISLOGICAL function returns 1 if the input is a logical scalar, series or array, else it returns 0.