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calculate_lookup_table_values [2025/12/22 15:51]
admin created 		calculate_lookup_table_values [2026/07/15 01:19] (current)
hermann
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 ===== Description ===== ===== Description =====
  
-This functor generates ​a new lookup table using keys from a base table and calculating ​values ​from a specified ​expression ​that can reference other tables and values.+Generates ​a new lookup table by evaluating an expression **once per row** of a base lookup table. The keys of the output table are inherited ​from the base table; the values ​are computed by the expression. 
 + 
 +This functor is one of five in the [[calculate_functors|calculator family]]. Use it when you need to recompute the values ​of an existing lookup table row by row, keeping the same key structure. If you also need to recompute the keys, use [[Calculate Lookup Table Keys And Values]] instead. 
 + 
 +The **abbreviated syntax** (also called **shorthand**) for this functor is ''​%''​. See [[ego_script#​calculator_functor_shorthand|Calculator functor shorthand]] in the EGO Script documentation for the full syntax of both the verbose and abbreviated forms, and [[calculate_functors|Calculate Functors — Complete Operator Documentation]] for the complete expression language reference.
  
 ===== Inputs ===== ===== Inputs =====
  
-^ Name  ^ Type  ^ Description ​ ^ +^ Name ^ Type ^ Description ^ 
-| Value Column Expression | [[Image Expression Type]] ​ | Expression describing how each new value should ​be calculated.  |+| Value Column Expression | [[Image Expression Type]] | The formula evaluated for each row. The result becomes the value for that row's key in the output table. Must be enclosed in square brackets ''​[ ]''​ in EGO Script. |
  
 ===== Optional Inputs ===== ===== Optional Inputs =====
  
-^ Name  ^ Type  ^ Description ​ ^ Default Value  ​^ +^ Name ^ Type ^ Default ​^ Description ^ 
-| Key Column Name  | [[Name Type]] ​ | Name of the key column. If omitted, the corresponding name from the table used as format will be used.  | None  ​| +| Key Column Name | [[Name Type]] ​| None | Name of the key column ​in the output lookup table. If omitted, the corresponding name from the base table is used. | 
-| Value Column Name  | [[Name Type]] ​ | Name of the value column. If omitted, the corresponding name from the table used as format will be used.  | None  ​| +| Value Column Name | [[Name Type]] ​| None | Name of the value column ​in the output lookup table. If omitted, the corresponding name from the base table is used. | 
-| Base Lookup Table  | [[Lookup Table Type]] ​ | Lookup ​table that, if provided, ​determines for which entries ​the value generation expression will be called. If this table is not provided, the table in the list of input tables ​with the smallest identifier value will be used.  | None  ​|+| Base Lookup Table | [[Lookup Table Type]] | None | The lookup ​table whose key set drives iteration. When not provided, the [[Number Table]] hook with the lowest list index that is connected to a **lookup table** (not a regular table) is used as the row source (verbose form), or the first lookup ​table referenced by name in the expression (abbreviated form) — not a union of all connected ​tables. Prefer this port over a ''​Number Table''​ hook when the table is needed only to define the row set and is not referenced in the expression, to keep abbreviated syntax available. |
  
 ===== Output ===== ===== Output =====
  
-^ Name  ^ Type  ^ Description ​ ^ +^ Name ^ Type ^ Description ^ 
-| Result ​ | [[Lookup Table Type]] ​ | Lookup ​table calculated ​from the input tables ​and values. ​ |+| Result | [[Lookup Table Type]] | A lookup ​table with keys from the base table and values ​computed by the expression. |
  
 ===== Group ===== ===== Group =====
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 ===== Notes ===== ===== Notes =====
  
-For each key present ​in the base lookup ​table, a key-value pair will be created ​and inserted into the resulting ​table. ​Keys are preserved from the base table, ​while values ​are calculated ​using the provided expression. The values of the key and value columns ​from the table used as format will be accessible during calculation as "​line" ​and "​column"​, respectively, in the expressions ​for calculating values of the resulting lookup table.+==== 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''​. 
 + 
 +==== Row iteration context ==== 
 + 
 +The expression is evaluated once per row of the base lookup ​table. ​Two keywords reflect the current row inside the expression:​ 
 + 
 +  * ''​line''​ — the **key** of the current row 
 +  * ''​column''​ — the **value already associated with that key** in the base lookup ​table 
 + 
 +This allows the expression to read the row's existing value directly via ''​column''​, and to look up related ​values ​from other connected tables ​using the current row's key — for example, ''​t1[line]''​ retrieves ​the value from table ''​t1''​ whose key matches the current row. 
 + 
 +==== Available expression features ==== 
 + 
 +Image operators (''​iX''​),​ neighbourhood functions, neighbourhood indexing, ​and convolution are not available — there is no spatial grid. Available features are arithmetic and logical operators, scalar references (''​vX''​), table and lookup table queries (''​tX[...]''​) ​in all single-key and multi-column forms, and the ''​line''​ and ''​column''​ row-context keywords. See [[calculate_functors#​the_expression_language|The Expression Language]] ​for the complete reference, or [[Image Expression Type]] for the navigable operator index. 
 + 
 +==== Null value handling ==== 
 + 
 +Null propagation rules and defensive patterns are covered in [[calculate_functors#​null_value_handling|Null Value Handling]] in the Calculate Functors documentation.
  
 ===== Internal Name ===== ===== Internal Name =====
  
-CalculateLookupTableValues+''​CalculateLookupTableValues''​