Package noaa.coastwatch.util.chunk

Class ExpressionFunction

java.lang.Object

noaa.coastwatch.util.chunk.ExpressionFunction

All Implemented Interfaces:

ChunkFunction

public class ExpressionFunction
extends Object
implements ChunkFunction

The ExpressionFunction class implements the ChunkFunction interface to perform mathematical expression calculations on chunk data.

Since:

3.4.0

Author:

Peter Hollemans

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	ExpressionFunction.VariableValueSource	Provides expression variable values for this function to run.

Constructor Summary

Constructors

Constructor	Description
ExpressionFunction()

Method Summary

Modifier and Type	Method	Description
DataChunk	apply(List<DataChunk> inputChunks)	Applies some function to a list of chunks.
void	init(ExpressionParser parser, DataChunk resultPrototype)	Initializes this function with the specified parser that will be used to evaluate expression values.
void	setSkipMissing(boolean flag)	Sets the skip missing flag (by default set to false).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ExpressionFunction

public ExpressionFunction()

Method Details

setSkipMissing

public void setSkipMissing(boolean flag)

Sets the skip missing flag (by default set to false).

Parameters:

flag - the new flag value. When the skip missing flag is set to true, the expression is not evaluated at all if any of the input values are set to missing. This has the advantage of saving computation time. When the flag is set to false, the expression is always evaluated and any missing values are used in the computation. This is important in cases when the expression includes a test for missing values such as an isNaN test, or if the data contains missing values that should actually be used in a computation (in some cases, flag variables are assigned a missing value of zero when they shouldn't be). Essentially the skip missing flag acts as an optimization in certain cases.

init

public void init(ExpressionParser parser,
 DataChunk resultPrototype)

Initializes this function with the specified parser that will be used to evaluate expression values. The parser should be initialized and the expression parsed before calling this method.

Parameters:

parser - the initialized and parsed expression parser.

resultPrototype - the result chunk prototype. The prototype will be used to generate new results when the apply(java.util.List<noaa.coastwatch.util.chunk.DataChunk>) method is called.

apply

public DataChunk apply(List<DataChunk> inputChunks)

Description copied from interface: ChunkFunction

Applies some function to a list of chunks.

Specified by:

apply in interface ChunkFunction

Parameters:

inputChunks - the list of chunks as input to the function.

Returns:

the output chunk of the function, or null if no valid output chunk could be computed.