Package uk.ac.starlink.topcat
Class SyntheticColumn
- java.lang.Object
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- uk.ac.starlink.table.ColumnData
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- uk.ac.starlink.topcat.SyntheticColumn
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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
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Constructor Summary
Constructors Constructor Description SyntheticColumn(TopcatModel tcModel, uk.ac.starlink.table.ColumnInfo cinfo, java.lang.String expression, java.lang.Class<?> resultType)
Constructs a new synthetic column from an algebraic expression applied to a table.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description java.lang.String
getExpression()
Returns the JEL expression that provides this column's value.java.lang.Object
readValue(long lrow)
void
setExpression(java.lang.String expression, java.lang.Class<?> resultType)
Sets the algebraic expression which this column uses to calculate its results.
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Constructor Detail
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SyntheticColumn
public SyntheticColumn(TopcatModel tcModel, uk.ac.starlink.table.ColumnInfo cinfo, java.lang.String expression, java.lang.Class<?> resultType) throws gnu.jel.CompilationException
Constructs a new synthetic column from an algebraic expression applied to a table.- Parameters:
tcModel
- context for JEL expression evaluationcinfo
- metadata for the new column; note this object may be modified as required by the supplied expressionexpression
- algebraic expression for the value of this columnresultType
- a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.- Throws:
gnu.jel.CompilationException
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Method Detail
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setExpression
public void setExpression(java.lang.String expression, java.lang.Class<?> resultType) 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 columnsresultType
- a Class for the result, presumably one of the primitive wrapper types or String.class. If null a suitable class is chosen automatically.- Throws:
gnu.jel.CompilationException
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getExpression
public java.lang.String getExpression()
Returns the JEL expression that provides this column's value.- Returns:
- expression
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readValue
public java.lang.Object readValue(long lrow) throws java.io.IOException
- Specified by:
readValue
in classuk.ac.starlink.table.ColumnData
- Throws:
java.io.IOException
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