transposeIntoArray( r ) {

		const m = this.elements;

		r[ 0 ] = m[ 0 ];
		r[ 1 ] = m[ 3 ];
		r[ 2 ] = m[ 6 ];
		r[ 3 ] = m[ 1 ];
		r[ 4 ] = m[ 4 ];
		r[ 5 ] = m[ 7 ];
		r[ 6 ] = m[ 2 ];
		r[ 7 ] = m[ 5 ];
		r[ 8 ] = m[ 8 ];

		return this;

	}
Transposes this matrix into the supplied array, and returns itself unchanged.

@param {Array<number>} r - An array to store the transposed matrix elements.
@return {Matrix3} A reference to this matrix.