SyntheticColumn (Starjava TOPCAT API)

java.lang.Object
- uk.ac.starlink.table.ColumnData
- - uk.ac.starlink.topcat.SyntheticColumn

```
public class SyntheticColumn
extends uk.ac.starlink.table.ColumnData
```
A column which produces read-only values based on an algebraic expression. This expression may include other columns in the table referenced by column name, and can use any of the java language expression constructs as well as the static methods in the java.lang.Math class. This list could be extended quite easily if new arithmetic tricks were required.
The engine used for expression evaluation is the GNU Java Expressions Library (JEL).

Author:

Mark Taylor (Starlink)

See Also:

JEL

Constructor Summary

Constructors
Constructor	Description
`SyntheticColumn(uk.ac.starlink.table.ValueInfo vinfo, java.lang.String expression, java.lang.Class resultType, uk.ac.starlink.ttools.jel.RandomJELRowReader rowReader)`	Constructs a new synthetic column from an algebraic expression applied to a table.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`java.lang.Object`	`readValue(long lrow)`
`void`	`setExpression(java.lang.String expression, java.lang.Class resultType, uk.ac.starlink.ttools.jel.RandomJELRowReader rowReader)`	Sets the algebraic expression which this column uses to calculate its results.

Methods inherited from class uk.ac.starlink.table.ColumnData
getColumnInfo, isWritable, setColumnInfo, storeValue

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - SyntheticColumn
```
public SyntheticColumn(uk.ac.starlink.table.ValueInfo vinfo,
                       java.lang.String expression,
                       java.lang.Class resultType,
                       uk.ac.starlink.ttools.jel.RandomJELRowReader rowReader)
                throws gnu.jel.CompilationException
```
    Constructs a new synthetic column from an algebraic expression applied to a table.
    
    Parameters:
    
    vinfo - template for the new column
    
    expression - algebraic expression for the value of this column
    
    resultType - a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.
    
    rowReader - context for JEL expression evaluation
    
    Throws:
    
    gnu.jel.CompilationException
- Method Detail
  - setExpression
```
public void setExpression(java.lang.String expression,
                          java.lang.Class resultType,
                          uk.ac.starlink.ttools.jel.RandomJELRowReader rowReader)
                   throws gnu.jel.CompilationException
```
    Sets the algebraic expression which this column uses to calculate its results. Column names are used to refer to values of cells in other columns of this table in the same row as that for which the result is being generated.
    
    Parameters:
    
    expression - the string giving the algebraic exprssion for this column's value in terms of other columns
    
    resultType - a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.
    
    rowReader - context for JEL expression evaluation
    
    Throws:
    
    gnu.jel.CompilationException
  - readValue
```
public java.lang.Object readValue(long lrow)
                           throws java.io.IOException
```
    Specified by:
    
    readValue in class uk.ac.starlink.table.ColumnData
    
    Throws:
    
    java.io.IOException

Class SyntheticColumn

Constructor Summary

Method Summary

Methods inherited from class uk.ac.starlink.table.ColumnData

Methods inherited from class java.lang.Object

Constructor Detail

SyntheticColumn

Method Detail

setExpression

readValue