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## weka.core
Class Instance

    java.lang.Object
      weka.core.Instance

All Implemented Interfaces:
  java.io.Serializable, Copyable

Direct Known Subclasses:
  IndividualInstance, SparseInstance

    public class Instance

extends java.lang.Object
implements Copyable, java.io.Serializable

Class for handling an instance. All values (numeric, date, nominal, or string) are internally stored as floating-point numbers. If an attribute is nominal (or a string), the stored value is the index of the corresponding nominal (or string) value in the attribute's definition. We have chosen this approach in favor of a more elegant object-oriented approach because it is much faster.

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

`...
// Create empty instance with three attribute values
Instance inst = new Instance(3);
// Set instance's values for the attributes "length", "weight", and "position"
inst.setValue(length, 5.3);
inst.setValue(weight, 300);
inst.setValue(position, "first");
// Set instance's dataset to be the dataset "race"
inst.setDataset(race);
// Print the instance
System.out.println("The instance: " + inst);
...
`

All methods that change an instance are safe, ie. a change of an instance does not affect any other instances. All methods that change an instance's attribute values clone the attribute value vector before it is changed. If your application heavily modifies instance values, it may be faster to create a new instance from scratch.

Version:
  $Revision: 1.19.2.2 $
Author:
  Eibe Frank (eibe@cs.waikato.ac.nz)
See Also:
  Serialized Form

Constructor Summary
`Instance(double weight, double[] attValues)` Constructor that inititalizes instance variable with given values.
`Instance(int numAttributes)` Constructor of an instance that sets weight to one, all values to be missing, and the reference to the dataset to null.

Method Summary
`Attribute` | `attribute(int index)` Returns the attribute with the given index.
`Attribute` | `attributeSparse(int indexOfIndex)` Returns the attribute with the given index.
`Attribute` | `classAttribute()` Returns class attribute.
`int` | `classIndex()` Returns the class attribute's index.
`boolean` | `classIsMissing()` Tests if an instance's class is missing.
`double` | `classValue()` Returns an instance's class value in internal format.
`java.lang.Object` | `copy()` Produces a shallow copy of this instance.
`Instances` | `dataset()` Returns the dataset this instance has access to.
`void` | `deleteAttributeAt(int position)` Deletes an attribute at the given position (0 to numAttributes() - 1).
`java.util.Enumeration` | `enumerateAttributes()` Returns an enumeration of all the attributes.
`boolean` | `equalHeaders(Instance inst)` Tests if the headers of two instances are equivalent.
`boolean` | `hasMissingValue()` Tests whether an instance has a missing value.
`int` | `index(int position)` Returns the index of the attribute stored at the given position.
`void` | `insertAttributeAt(int position)` Inserts an attribute at the given position (0 to numAttributes()).
`boolean` | `isMissing(Attribute att)` Tests if a specific value is "missing".
`boolean` | `isMissing(int attIndex)` Tests if a specific value is "missing".
`boolean` | `isMissingSparse(int indexOfIndex)` Tests if a specific value is "missing".
`static boolean` | `isMissingValue(double val)` Tests if the given value codes "missing".
`static void` | `main(java.lang.String[] options)` Main method for testing this class.
`Instance` | `mergeInstance(Instance inst)` Merges this instance with the given instance and returns the result.
`static double` | `missingValue()` Returns the double that codes "missing".
`int` | `numAttributes()` Returns the number of attributes.
`int` | `numClasses()` Returns the number of class labels.
`int` | `numValues()` Returns the number of values present.
`void` | `replaceMissingValues(double[] array)` Replaces all missing values in the instance with the values contained in the given array.
`void` | `setClassMissing()` Sets the class value of an instance to be "missing".
`void` | `setClassValue(double value)` Sets the class value of an instance to the given value (internal floating-point format).
`void` | `setClassValue(java.lang.String value)` Sets the class value of an instance to the given value.
`void` | `setDataset(Instances instances)` Sets the reference to the dataset.
`void` | `setMissing(Attribute att)` Sets a specific value to be "missing".
`void` | `setMissing(int attIndex)` Sets a specific value to be "missing".
`void` | `setValue(Attribute att, double value)` Sets a specific value in the instance to the given value (internal floating-point format).
`void` | `setValue(Attribute att, java.lang.String value)` Sets a value of an nominal or string attribute to the given value.
`void` | `setValue(int attIndex, double value)` Sets a specific value in the instance to the given value (internal floating-point format).
`void` | `setValue(int attIndex, java.lang.String value)` Sets a value of a nominal or string attribute to the given value.
`void` | `setValueSparse(int indexOfIndex, double value)` Sets a specific value in the instance to the given value (internal floating-point format).
`void` | `setWeight(double weight)` Sets the weight of an instance.
`java.lang.String` | `stringValue(Attribute att)` Returns the string value of a nominal, string, or date attribute for the instance.
`java.lang.String` | `stringValue(int attIndex)` Returns the string value of a nominal, string, or date attribute for the instance.
`double[]` | `toDoubleArray()` Returns the values of each attribute as an array of doubles.
`java.lang.String` | `toString()` Returns the description of one instance.
`java.lang.String` | `toString(Attribute att)` Returns the description of one value of the instance as a string.
`java.lang.String` | `toString(int attIndex)` Returns the description of one value of the instance as a string.
`double` | `value(Attribute att)` Returns an instance's attribute value in internal format.
`double` | `value(int attIndex)` Returns an instance's attribute value in internal format.
`double` | `valueSparse(int indexOfIndex)` Returns an instance's attribute value in internal format.
`double` | `weight()` Returns the instance's weight.

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

### Instance

    public Instance(double weight,
                    double[] attValues)

  Constructor that inititalizes instance variable with given values. Reference to the dataset is set to null. (ie. the instance doesn't have access to information about the attribute types)

  Parameters:
    `weight` - the instance's weight
    `attValues` - a vector of attribute values

### Instance

    public Instance(int numAttributes)

  Constructor of an instance that sets weight to one, all values to be missing, and the reference to the dataset to null. (ie. the instance doesn't have access to information about the attribute types)

  Parameters:
    `numAttributes` - the size of the instance

Method Detail

### attribute

    public Attribute attribute(int index)

  Returns the attribute with the given index.

  Parameters:
    `index` - the attribute's index
  Returns:
    the attribute at the given position
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to a dataset

### attributeSparse

    public Attribute attributeSparse(int indexOfIndex)

  Returns the attribute with the given index. Does the same thing as attribute().

  Parameters:
    `indexOfIndex` - the index of the attribute's index
  Returns:
    the attribute at the given position
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to a dataset

### classAttribute

    public Attribute classAttribute()

  Returns class attribute.

  Returns:
    the class attribute
  Throws:
    `UnassignedDatasetException` - if the class is not set or the instance doesn't have access to a dataset

### classIndex

    public int classIndex()

  Returns the class attribute's index.

  Returns:
    the class index as an integer
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to a dataset

### classIsMissing

    public boolean classIsMissing()

  Tests if an instance's class is missing.

  Returns:
    true if the instance's class is missing
  Throws:
    `UnassignedClassException` - if the class is not set or the instance doesn't have access to a dataset

### classValue

    public double classValue()

  Returns an instance's class value in internal format. (ie. as a floating-point number)

  Returns:
    the corresponding value as a double (If the corresponding attribute is nominal (or a string) then it returns the value's index as a double).
  Throws:
    `UnassignedClassException` - if the class is not set or the instance doesn't have access to a dataset

### copy

    public java.lang.Object copy()

  Produces a shallow copy of this instance. The copy has access to the same dataset. (if you want to make a copy that doesn't have access to the dataset, use `new Instance(instance)`

  Specified by:
    `copy` in interface `Copyable`
  Returns:
    the shallow copy

### dataset

    public Instances dataset()

  Returns the dataset this instance has access to. (ie. obtains information about attribute types from) Null if the instance doesn't have access to a dataset.

  Returns:
    the dataset the instance has accesss to

### deleteAttributeAt

    public void deleteAttributeAt(int position)

  Deletes an attribute at the given position (0 to numAttributes() - 1). Only succeeds if the instance does not have access to any dataset because otherwise inconsistencies could be introduced.

  Parameters:
    `pos` - the attribute's position
  Throws:
    `java.lang.RuntimeException` - if the instance has access to a dataset

### enumerateAttributes

    public java.util.Enumeration enumerateAttributes()

  Returns an enumeration of all the attributes.

  Returns:
    enumeration of all the attributes
  Throws:
    `UnassignedDatasetException` - if the instance doesn't have access to a dataset

### equalHeaders

    public boolean equalHeaders(Instance inst)

  Tests if the headers of two instances are equivalent.

  Parameters:
    `instance` - another instance
  Returns:
    true if the header of the given instance is equivalent to this instance's header
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to any dataset

### hasMissingValue

    public boolean hasMissingValue()

  Tests whether an instance has a missing value. Skips the class attribute if set.

  Returns:
    true if instance has a missing value.
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to any dataset

### index

    public int index(int position)

  Returns the index of the attribute stored at the given position. Just returns the given value.

  Parameters:
    `position` - the position
  Returns:
    the index of the attribute stored at the given position

### insertAttributeAt

    public void insertAttributeAt(int position)

  Inserts an attribute at the given position (0 to numAttributes()). Only succeeds if the instance does not have access to any dataset because otherwise inconsistencies could be introduced.

  Parameters:
    `pos` - the attribute's position
  Throws:
    `java.lang.RuntimeException` - if the instance has accesss to a dataset
    `java.lang.IllegalArgumentException` - if the position is out of range

### isMissing

    public boolean isMissing(int attIndex)

  Tests if a specific value is "missing".

  Parameters:
    `attIndex` - the attribute's index

### isMissingSparse

    public boolean isMissingSparse(int indexOfIndex)

  Tests if a specific value is "missing". Does the same thing as isMissing() if applied to an Instance.

  Parameters:
    `indexOfIndex` - the index of the attribute's index

### isMissing

    public boolean isMissing(Attribute att)

  Tests if a specific value is "missing". The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute

### isMissingValue

    public static boolean isMissingValue(double val)

  Tests if the given value codes "missing".

  Parameters:
    `val` - the value to be tested
  Returns:
    true if val codes "missing"

### mergeInstance

    public Instance mergeInstance(Instance inst)

  Merges this instance with the given instance and returns the result. Dataset is set to null.

  Parameters:
    `inst` - the instance to be merged with this one
  Returns:
    the merged instances

### missingValue

    public static double missingValue()

  Returns the double that codes "missing".

  Returns:
    the double that codes "missing"

### numAttributes

    public int numAttributes()

  Returns the number of attributes.

  Returns:
    the number of attributes as an integer

### numClasses

    public int numClasses()

  Returns the number of class labels.

  Returns:
    the number of class labels as an integer if the class attribute is nominal, 1 otherwise.
  Throws:
    `UnassignedDatasetException` - if instance doesn't have access to any dataset

### numValues

    public int numValues()

  Returns the number of values present. Always the same as numAttributes().

  Returns:
    the number of values

### replaceMissingValues

    public void replaceMissingValues(double[] array)

  Replaces all missing values in the instance with the values contained in the given array. A deep copy of the vector of attribute values is performed before the values are replaced.

  Parameters:
    `array` - containing the means and modes
  Throws:
    `java.lang.IllegalArgumentException` - if numbers of attributes are unequal

### setClassMissing

    public void setClassMissing()

  Sets the class value of an instance to be "missing". A deep copy of the vector of attribute values is performed before the value is set to be missing.

  Throws:
    `UnassignedClassException` - if the class is not set
    `UnassignedDatasetException` - if the instance doesn't have access to a dataset

### setClassValue

    public void setClassValue(double value)

  Sets the class value of an instance to the given value (internal floating-point format). A deep copy of the vector of attribute values is performed before the value is set.

  Parameters:
    `value` - the new attribute value (If the corresponding attribute is nominal (or a string) then this is the new value's index as a double).
  Throws:
    `UnassignedClassException` - if the class is not set
    `UnaddignedDatasetException` - if the instance doesn't have access to a dataset

### setClassValue

    public final void setClassValue(java.lang.String value)

  Sets the class value of an instance to the given value. A deep copy of the vector of attribute values is performed before the value is set.

  Parameters:
    `value` - the new class value (If the class is a string attribute and the value can't be found, the value is added to the attribute).
  Throws:
    `UnassignedClassException` - if the class is not set
    `UnassignedDatasetException` - if the dataset is not set
    `java.lang.IllegalArgumentException` - if the attribute is not nominal or a string, or the value couldn't be found for a nominal attribute

### setDataset

    public final void setDataset(Instances instances)

  Sets the reference to the dataset. Does not check if the instance is compatible with the dataset. Note: the dataset does not know about this instance. If the structure of the dataset's header gets changed, this instance will not be adjusted automatically.

  Parameters:
    `instances` - the reference to the dataset

### setMissing

    public final void setMissing(int attIndex)

  Sets a specific value to be "missing". Performs a deep copy of the vector of attribute values before the value is set to be missing.

  Parameters:
    `attIndex` - the attribute's index

### setMissing

    public final void setMissing(Attribute att)

  Sets a specific value to be "missing". Performs a deep copy of the vector of attribute values before the value is set to be missing. The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute

### setValue

    public void setValue(int attIndex,
                         double value)

  Sets a specific value in the instance to the given value (internal floating-point format). Performs a deep copy of the vector of attribute values before the value is set.

  Parameters:
    `attIndex` - the attribute's index
    `value` - the new attribute value (If the corresponding attribute is nominal (or a string) then this is the new value's index as a double).

### setValueSparse

    public void setValueSparse(int indexOfIndex,
                               double value)

  Sets a specific value in the instance to the given value (internal floating-point format). Performs a deep copy of the vector of attribute values before the value is set. Does exactly the same thing as setValue().

  Parameters:
    `indexOfIndex` - the index of the attribute's index
    `value` - the new attribute value (If the corresponding attribute is nominal (or a string) then this is the new value's index as a double).

### setValue

    public final void setValue(int attIndex,
                               java.lang.String value)

  Sets a value of a nominal or string attribute to the given value. Performs a deep copy of the vector of attribute values before the value is set.

  Parameters:
    `attIndex` - the attribute's index
    `value` - the new attribute value (If the attribute is a string attribute and the value can't be found, the value is added to the attribute).
  Throws:
    `UnassignedDatasetException` - if the dataset is not set
    `java.lang.IllegalArgumentException` - if the selected attribute is not nominal or a string, or the supplied value couldn't be found for a nominal attribute

### setValue

    public final void setValue(Attribute att,
                               double value)

  Sets a specific value in the instance to the given value (internal floating-point format). Performs a deep copy of the vector of attribute values before the value is set, so if you are planning on calling setValue many times it may be faster to create a new instance using toDoubleArray. The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute
    `value` - the new attribute value (If the corresponding attribute is nominal (or a string) then this is the new value's index as a double).

### setValue

    public final void setValue(Attribute att,
                               java.lang.String value)

  Sets a value of an nominal or string attribute to the given value. Performs a deep copy of the vector of attribute values before the value is set, so if you are planning on calling setValue many times it may be faster to create a new instance using toDoubleArray. The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute
    `value` - the new attribute value (If the attribute is a string attribute and the value can't be found, the value is added to the attribute).
  Throws:
    `java.lang.IllegalArgumentException` - if the the attribute is not nominal or a string, or the value couldn't be found for a nominal attribute

### setWeight

    public final void setWeight(double weight)

  Sets the weight of an instance.

  Parameters:
    `weight` - the weight

### stringValue

    public final java.lang.String stringValue(int attIndex)

  Returns the string value of a nominal, string, or date attribute for the instance.

  Parameters:
    `attIndex` - the attribute's index
  Returns:
    the value as a string
  Throws:
    `java.lang.IllegalArgumentException` - if the attribute is not a nominal, string, or date attribute.
    `UnassignedDatasetException` - if the instance doesn't belong to a dataset.

### stringValue

    public final java.lang.String stringValue(Attribute att)

  Returns the string value of a nominal, string, or date attribute for the instance.

  Parameters:
    `att` - the attribute
  Returns:
    the value as a string
  Throws:
    `java.lang.IllegalArgumentException` - if the attribute is not a nominal, string, or date attribute.
    `UnassignedDatasetException` - if the instance doesn't belong to a dataset.

### toDoubleArray

    public double[] toDoubleArray()

  Returns the values of each attribute as an array of doubles.

  Returns:
    an array containing all the instance attribute values

### toString

    public java.lang.String toString()

  Returns the description of one instance. If the instance doesn't have access to a dataset, it returns the internal floating-point values. Quotes string values that contain whitespace characters.

  Overrides:
    `toString` in class `java.lang.Object`
  Returns:
    the instance's description as a string

### toString

    public final java.lang.String toString(int attIndex)

  Returns the description of one value of the instance as a string. If the instance doesn't have access to a dataset, it returns the internal floating-point value. Quotes string values that contain whitespace characters, or if they are a question mark.

  Parameters:
    `attIndex` - the attribute's index
  Returns:
    the value's description as a string

### toString

    public final java.lang.String toString(Attribute att)

  Returns the description of one value of the instance as a string. If the instance doesn't have access to a dataset it returns the internal floating-point value. Quotes string values that contain whitespace characters, or if they are a question mark. The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute
  Returns:
    the value's description as a string

### value

    public double value(int attIndex)

  Returns an instance's attribute value in internal format.

  Parameters:
    `attIndex` - the attribute's index
  Returns:
    the specified value as a double (If the corresponding attribute is nominal (or a string) then it returns the value's index as a double).

### valueSparse

    public double valueSparse(int indexOfIndex)

  Returns an instance's attribute value in internal format. Does exactly the same thing as value() if applied to an Instance.

  Parameters:
    `indexOfIndex` - the index of the attribute's index
  Returns:
    the specified value as a double (If the corresponding attribute is nominal (or a string) then it returns the value's index as a double).

### value

    public double value(Attribute att)

  Returns an instance's attribute value in internal format. The given attribute has to belong to a dataset.

  Parameters:
    `att` - the attribute
  Returns:
    the specified value as a double (If the corresponding attribute is nominal (or a string) then it returns the value's index as a double).

### weight

    public final double weight()

  Returns the instance's weight.

  Returns:
    the instance's weight as a double

### main

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

  Main method for testing this class.

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