weka.core
Class Attribute

java.lang.Object
  weka.core.Attribute

All Implemented Interfaces:

java.io.Serializable, Copyable

public class Attribute
extends java.lang.Object
implements Copyable, java.io.Serializable

Class for handling an attribute. Once an attribute has been created, it can't be changed.

Three attribute types are supported:

• numeric:
  This type of attribute represents a floating-point number.
• nominal:
  This type of attribute represents a fixed set of nominal values.
• string:
  This type of attribute represents a dynamically expanding set of nominal values. String attributes are not used by the learning schemes in Weka. They can be used, for example, to store an identifier with each instance in a dataset.

Typical usage (code from the main() method of this class):

...
// Create numeric attributes "length" and "weight"
Attribute length = new Attribute("length");
Attribute weight = new Attribute("weight");

// Create vector to hold nominal values "first", "second", "third"
FastVector my_nominal_values = new FastVector(3);
my_nominal_values.addElement("first");
my_nominal_values.addElement("second");
my_nominal_values.addElement("third");

// Create nominal attribute "position"
Attribute position = new Attribute("position", my_nominal_values);
...


Version:

$Revision: 1.1 $

Author:

Eibe Frank ([email protected])

See Also:

Serialized Form

Field Summary

static int	NOMINAL Constant set for nominal attributes.
static int	NUMERIC Constant set for numeric attributes.
static int	STRING Constant set for attributes with string values.

Constructor Summary

Attribute(java.lang.String attributeName)
Constructor for a numeric attribute.

Attribute(java.lang.String attributeName, FastVector attributeValues)
Constructor for nominal attributes and string attributes.

Method Summary

int	addStringValue(Attribute src, int index) Adds a string value to the list of valid strings for attributes of type STRING and returns the index of the string.
int	addStringValue(java.lang.String value) Adds a string value to the list of valid strings for attributes of type STRING and returns the index of the string.
java.lang.Object	copy() Produces a shallow copy of this attribute.
java.util.Enumeration	enumerateValues() Returns an enumeration of all the attribute's values if the attribute is nominal or a string, null otherwise.
boolean	equals(java.lang.Object other) Tests if given attribute is equal to this attribute.
int	index() Returns the index of this attribute.
int	indexOfValue(java.lang.String value) Returns the index of a given attribute value.
boolean	isNominal() Test if the attribute is nominal.
boolean	isNumeric() Tests if the attribute is numeric.
boolean	isString() Tests if the attribute is a string.
static void	main(java.lang.String[] ops) Simple main method for testing this class.
java.lang.String	name() Returns the attribute's name.
int	numValues() Returns the number of attribute values.
java.lang.String	toString() Returns a description of this attribute in ARFF format.
int	type() Returns the attribute's type as an integer.
java.lang.String	value(int valIndex) Returns a value of a nominal or string attribute.

Methods inherited from class java.lang.Object

getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

NUMERIC

public static final int NUMERIC

Constant set for numeric attributes.

See Also:

Constant Field Values

NOMINAL

public static final int NOMINAL

Constant set for nominal attributes.

See Also:

Constant Field Values

STRING

public static final int STRING

Constant set for attributes with string values.

See Also:

Constant Field Values

Constructor Detail

Attribute

public Attribute(java.lang.String attributeName)

Constructor for a numeric attribute.

Parameters:

attributeName - the name for the attribute

Attribute

public Attribute(java.lang.String attributeName,
                 FastVector attributeValues)

Constructor for nominal attributes and string attributes. If a null vector of attribute values is passed to the method, the attribute is assumed to be a string.

Parameters:

attributeName - the name for the attribute

attributeValues - a vector of strings denoting the attribute values. Null if the attribute is a string attribute.

Method Detail

copy

public java.lang.Object copy()

Produces a shallow copy of this attribute.

Specified by:

copy in interface Copyable

Returns:

a copy of this attribute with the same index

enumerateValues

public final java.util.Enumeration enumerateValues()

Returns an enumeration of all the attribute's values if the attribute is nominal or a string, null otherwise.

Returns:

enumeration of all the attribute's values

equals

public final boolean equals(java.lang.Object other)

Tests if given attribute is equal to this attribute.

Overrides:

equals in class java.lang.Object

Parameters:

other - the Object to be compared to this attribute

Returns:

true if the given attribute is equal to this attribute

index

public final int index()

Returns the index of this attribute.

Returns:

the index of this attribute

indexOfValue

public final int indexOfValue(java.lang.String value)

Returns the index of a given attribute value. (The index of the first occurence of this value.)

Parameters:

value - the value for which the index is to be returned

Returns:

the index of the given attribute value if attribute is nominal or a string, -1 if it is numeric or the value can't be found

isNominal

public final boolean isNominal()

Test if the attribute is nominal.

Returns:

true if the attribute is nominal

isNumeric

public final boolean isNumeric()

Tests if the attribute is numeric.

Returns:

true if the attribute is numeric

isString

public final boolean isString()

Tests if the attribute is a string.

Returns:

true if the attribute is a string

name

public final java.lang.String name()

Returns the attribute's name.

Returns:

the attribute's name as a string

numValues

public final int numValues()

Returns the number of attribute values. Returns 0 for numeric attributes.

Returns:

the number of attribute values

toString

public final java.lang.String toString()

Returns a description of this attribute in ARFF format. Quotes strings if they contain whitespace characters, or if they are a question mark.

Overrides:

toString in class java.lang.Object

Returns:

a description of this attribute as a string

type

public final int type()

Returns the attribute's type as an integer.

Returns:

the attribute's type.

value

public final java.lang.String value(int valIndex)

Returns a value of a nominal or string attribute. Returns an empty string if the attribute is neither nominal nor a string attribute.

Parameters:

valIndex - the value's index

Returns:

the attribute's value as a string

addStringValue

public int addStringValue(java.lang.String value)

Adds a string value to the list of valid strings for attributes of type STRING and returns the index of the string.

Parameters:

value - The string value to add

Returns:

the index assigned to the string, or -1 if the attribute is not of type Attribute.STRING

addStringValue

public int addStringValue(Attribute src,
                          int index)

Adds a string value to the list of valid strings for attributes of type STRING and returns the index of the string. This method is more efficient than addStringValue(String) for long strings.

Parameters:

src - The Attribute containing the string value to add.

index - the index of the string value in the source attribute.

Returns:

the index assigned to the string, or -1 if the attribute is not of type Attribute.STRING

main

public static void main(java.lang.String[] ops)

Simple main method for testing this class.