# mvpa2.algorithms.group_clusterthr.dok_matrix¶

class `mvpa2.algorithms.group_clusterthr.``dok_matrix`(arg1, shape=None, dtype=None, copy=False)

Dictionary Of Keys based sparse matrix.

This is an efficient structure for constructing sparse matrices incrementally.

This can be instantiated in several ways:
dok_matrix(D)
with a dense matrix, D
dok_matrix(S)
with a sparse matrix, S
dok_matrix((M,N), [dtype])
create the matrix with initial shape (M,N) dtype is optional, defaulting to dtype=’d’

Notes

Sparse matrices can be used in arithmetic operations: they support addition, subtraction, multiplication, division, and matrix power.

Allows for efficient O(1) access of individual elements. Duplicates are not allowed. Can be efficiently converted to a coo_matrix once constructed.

Examples

```>>> import numpy as np
>>> from scipy.sparse import dok_matrix
>>> S = dok_matrix((5, 5), dtype=np.float32)
>>> for i in range(5):
...     for j in range(5):
...         S[i, j] = i + j    # Update element
```

Attributes

 `shape` `ndim` `nnz`
 dtype dtype Data type of the matrix

Methods

 `clear`(() -> None.  Remove all items from D.) `fromkeys`(...) v defaults to None. `has_key`((k) -> True if D has a key k, else False) `items`(() -> list of D’s (key, value) pairs, ...) `iteritems`(() -> an iterator over the (key, ...) `iterkeys`(() -> an iterator over the keys of D) `itervalues`(...) `keys`(() -> list of D’s keys) `pop`((k[,d]) -> v, ...) If key is not found, d is returned if given, otherwise KeyError is raised `popitem`(() -> (k, v), ...) 2-tuple; but raise KeyError if D is empty. `setdefault`((k[,d]) -> D.get(k,d), ...) `update`(([E, ...) If E present and has a .keys() method, does: for k in E: D[k] = E[k] `values`(() -> list of D’s values) `viewitems`(...) `viewkeys`(...) `viewvalues`(...)
`conjtransp`()

Return the conjugate transpose

`copy`()
`get`(key, default=0.0)

This overrides the dict.get method, providing type checking but otherwise equivalent functionality.

`getcol`(j)

Returns a copy of column j of the matrix as a (m x 1) DOK matrix.

`getnnz`()
`getrow`(i)

Returns a copy of row i of the matrix as a (1 x n) DOK matrix.

`nnz`
`resize`(shape)

Resize the matrix in-place to dimensions given by ‘shape’.

Any non-zero elements that lie outside the new shape are removed.

`tocoo`()

Return a copy of this matrix in COOrdinate format

`tocsc`()

Return a copy of this matrix in Compressed Sparse Column format

`tocsr`()

Return a copy of this matrix in Compressed Sparse Row format

`todok`(copy=False)
`transpose`()

Return the transpose