Calculate Value

Description

Evaluates an algebraic or logical expression once and returns a single scalar value. Unlike the map and lookup table calculators, there is no current cell, row, or spatial grid: the expression is evaluated in a purely scalar context, drawing only on tables, lookup tables, and scalar values connected through hooks.

This is one of Dinamica EGO's five calculator functors. Its abbreviated (shorthand) syntax is $. See Calculator functor shorthand in the EGO Script documentation for the verbose and abbreviated forms, and Calculate Functors — Complete Operator Documentation for the full expression language reference.

Inputs

Name	Type	Description
Expression	Image Expression Type	Algebraic or logical expression that evaluates to a single numeric result. Must be enclosed in square brackets [ ] in EGO Script.

Optional Inputs

Name	Type	Description	Default Value
Default Value	Real Value Type	Value returned if evaluating the expression produces an algebraic error. When not provided, evaluation errors are propagated. This is an advanced port.	.none

Outputs

Name	Type	Description
Result	Real Value Type	The computed scalar value.

Group

Table

Notes

Connecting data inputs

Tables, lookup tables, and scalar values referenced in the expression must be connected to the functor's ports before writing the expression, using hook functors:

Tables and lookup tables → Number Table → referenced in the expression as t1, t2, …, t100

Scalar values → Number Value → referenced as v1, v2, …, v100

Maps cannot be connected — there is no cell context in this functor. In the abbreviated syntax, tables are referenced as %variableName and values as $variableName.

Available expression features

Image operators (iX), the line and column spatial keywords, neighbourhood functions, neighbourhood indexing, and convolution are not available — there is no cell or row context. Available features are arithmetic and logical operators and table and lookup table queries (tX[...]) in all single-key and multi-column forms. See The Expression Language for the complete reference, or Image Expression Type for the navigable operator index.

All operations are performed using the precision defined by ImageExpression::Value; the final result is then converted to a double-precision real. See Calculate Value 2 for a variant that instead performs all operations using double precision throughout.

Null value handling

Null propagation rules and defensive patterns are covered in Null Value Handling in the Calculate Functors documentation.

Internal Name

CalculateValue

Usage examples

CalculateValue practical examples in the Calculate Functors documentation

Lesson 8: Inserting and getting a specific value into a table