SRL missing value handling

Missing values are valueless variables, or variables without data. Missing values are also referred to as null values or empty variables. Missing values affect the outcome of various SRL operations and cause them to work differently than when working with non-null values.

If a number is missing, this does not mean the number is set to 0. It is kept as the special value "null". "null" and the number 0 are not the same value or strings, the empty string (a string without any characters like "") is not equal to null either. When you are looking at some data, PolyAnalyst does not display a null string value any differently than an empty "" string value. Both values appear as empty cells in the data grid. However, when working in SRL, the two values (null string versus empty string) are not equivalent.

The following examples use M to denote a missing value whereas A is a numeric value.

1) If one of the arguments of logical AND operation has a missing value, and the other one has the value No, then the resulting value is No:

  • 1 < M AND 1 > 2 returns No;

  • 1 < M AND 1 < 2 returns null.

2) If one of the arguments of logical OR operation has a missing value, and the other one has the value Yes, then the resulting value is Yes:

  • 1 < M OR 1 > 2 returns null;

  • 1 < M OR 1 < 2 returns Yes.

3) if one of the operation or function arguments has a missing value, the result is a missing value:

  • M + 1 returns null;

  • sin(M) returns null;

  • pow(A, M) returns null.