**'cern.colt.matrix.impl.SparseObjectMatrix2D'**Java class

## Class SparseObjectMatrix2D

- java.lang.Object
- cern.colt.PersistentObject
- cern.colt.matrix.impl.AbstractMatrix
- cern.colt.matrix.impl.AbstractMatrix2D
- cern.colt.matrix.ObjectMatrix2D
- cern.colt.matrix.impl.SparseObjectMatrix2D

- All Implemented Interfaces:
- Serializable, Cloneable

public class SparseObjectMatrix2Dextends ObjectMatrix2D

Sparse hashed 2-d matrix holding`Object`elements.First see the package summary and javadoc tree view to get the broad picture.**Implementation:**Note that this implementation is not synchronized.Uses a

`OpenIntObjectHashMap`

, which is a compact and performant hashing technique.**Memory requirements:**Cells that

- are never set to non-zero values do not use any memory.
- switch from zero to non-zero state do use memory.
- switch back from non-zero to zero state also do use memory. However, their memory is automatically reclaimed from time to time. It can also manually be reclaimed by calling
`trimToSize()`

.

worst case:

`memory [bytes] = (1/minLoadFactor) * nonZeros * 13`.

best case:`memory [bytes] = (1/maxLoadFactor) * nonZeros * 13`.

Where`nonZeros = cardinality()`is the number of non-zero cells.Thus, a 1000 x 1000 matrix with minLoadFactor=0.25 and maxLoadFactor=0.5 and 1000000 non-zero cells consumes between 25 MB and 50 MB.The same 1000 x 1000 matrix with 1000 non-zero cells consumes between 25 and 50 KB.**Time complexity:**This class offers

*expected*time complexity`O(1)`(i.e. constant time) for the basic operations`get`,`getQuick`,`set`,`setQuick`and`size`assuming the hash function disperses the elements properly among the buckets.Otherwise, pathological cases, although highly improbable, can occur, degrading performance to`O(N)`in the worst case.As such this sparse class is expected to have no worse time complexity than its dense counterpart`DenseObjectMatrix2D`

.However, constant factors are considerably larger.Cells are internally addressed in row-major.Performance sensitive applications can exploit this fact.Setting values in a loop row-by-row is quicker than column-by-column, because fewer hash collisions occur.Thus

for (int row=0; row < rows; row++) { for (int column=0; column < columns; column++) { matrix.setQuick(row,column,someValue); } }

is quicker thanfor (int column=0; column < columns; column++) { for (int row=0; row < rows; row++) { matrix.setQuick(row,column,someValue); } }

- See Also:
`cern.colt.map`

,`OpenIntObjectHashMap`

, Serialized Form

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