3.6. Operations on rows and columns

3.6.1. igraph_matrix_get_row — Extract a row
3.6.2. igraph_matrix_get_col — Select a column
3.6.3. igraph_matrix_set_row — Set a row from a vector.
3.6.4. igraph_matrix_set_col — Set a column from a vector.
3.6.5. igraph_matrix_swap_rows — Swap two rows
3.6.6. igraph_matrix_swap_cols — Swap two columns
3.6.7. igraph_matrix_select_rows — Select some rows of a matrix
3.6.8. igraph_matrix_select_cols — Select some columns of a matrix

3.6.1. `igraph_matrix_get_row` — Extract a row

int igraph_matrix_get_row(const igraph_matrix_t *m, 
				    igraph_vector_t *res, long int index);

Extract a row from a matrix and return it as a vector.

Arguments:

`m`:	The input matrix.
`res`:	Pointer to an initialized vector, it will be resized if needed.
`index`:	The index of the row to select.

Returns:

Error code.

Time complexity: O(n), the number of columns in the matrix.

3.6.2. `igraph_matrix_get_col` — Select a column

int igraph_matrix_get_col(const igraph_matrix_t *m, 
				    igraph_vector_t *res,
				    long int index);

Extract a column of a matrix and return it in a vector.

Arguments:

`m`:	The input matrix.
`res`:	The result will we stored in this vector. It should be initialized and will be resized as needed.
`index`:	The index of the solumn to select.

Returns:

Error code.

Time complexity: O(n), the number of rows in the matrix.

3.6.3. `igraph_matrix_set_row` — Set a row from a vector.

int igraph_matrix_set_row(igraph_matrix_t *m,
				    const igraph_vector_t *v, long int index);

Sets the elements of a row, from the given vector. The length of the vector and the number of columns in the matrix must match, otherwise and error is triggered.

Arguments:

`m`:	The input matrix.
`v`:	The vector containing the new elements of the row.
`index`:	Index of the row to set.

Returns:

Error code.

Time complexity: O(n), the number of columns in the matrix.

3.6.4. `igraph_matrix_set_col` — Set a column from a vector.

int igraph_matrix_set_col(igraph_matrix_t *m,
				    const igraph_vector_t *v, long int index);

Sets the elements of a column, from the given vector. The length of the vector and the number of rows in the matrix must match, otherwise and error is triggered.

Arguments:

`m`:	The input matrix.
`v`:	The vector containing the new elements of the column.
`index`:	Index of the column to set.

Returns:

Error code.

Time complexity: O(m), the number of rows in the matrix.

3.6.5. `igraph_matrix_swap_rows` — Swap two rows

int igraph_matrix_swap_rows(igraph_matrix_t *m, 
				      long int i, long int j);

Swap two rows in the matrix.

Arguments:

`m`:	The input matrix.
`i`:	The index of the first row.
`j`:	The index of the second row.

Returns:

Error code.

Time complexity: O(n), the number of columns.

3.6.6. `igraph_matrix_swap_cols` — Swap two columns

int igraph_matrix_swap_cols(igraph_matrix_t *m, 
				      long int i, long int j);

Swap two columns in the matrix.

Arguments:

`m`:	The input matrix.
`i`:	The index of the first column.
`j`:	The index of the second column.

Returns:

Error code.

Time complexity: O(m), the number of rows.

3.6.7. `igraph_matrix_select_rows` — Select some rows of a matrix

int igraph_matrix_select_rows(const igraph_matrix_t *m, 
					igraph_matrix_t *res, 
					const igraph_vector_t *rows);

This function selects some rows of a matrix and returns them in a new matrix. The result matrix should be initialized before calling the function.

Arguments:

`m`:	The input matrix.
`res`:	The result matrix. It should be initialized and will be resized as needed.
`rows`:	Vector, it contains the row indices (starting with zero) to extract. Note that no range checking is performed.

Returns:

Error code.

Time complexity: O(nm), n is the number of rows, m the number of columns of the result matrix.

3.6.8. `igraph_matrix_select_cols` — Select some columns of a matrix

int igraph_matrix_select_cols(const igraph_matrix_t *m,
					igraph_matrix_t *res, 
					const igraph_vector_t *cols);

This function selects some columns of a matrix and returns them in a new matrix. The result matrix should be initialized before calling the function.

Arguments:

`m`:	The input matrix.
`res`:	The result matrix. It should be initialized and will be resized as needed.
`cols`:	Vector, it contains the column indices (starting with zero) to extract. Note that no range checking is performed.

Returns:

Error code.

Time complexity: O(nm), n is the number of rows, m the number of columns of the result matrix.