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# skbio.stats.distance.DistanceMatrix.__getitem__

`DistanceMatrix.``__getitem__`(index)

  Slice into dissimilarity data by object ID or numpy indexing.

  State: Experimental as of 0.4.0.

  Extracts data from the dissimilarity matrix by object ID, a pair of IDs, or numpy indexing/slicing.

  Parameters:

  index (str, two-tuple of str, or numpy index) –

  index can be one of the following forms: an ID, a pair of IDs, or a numpy index.

  If index is a string, it is assumed to be an ID and a `numpy.ndarray` row vector is returned for the corresponding ID. Note that the ID’s row of dissimilarities is returned, not its column. If the matrix is symmetric, the two will be identical, but this makes a difference if the matrix is asymmetric.

  If index is a two-tuple of strings, each string is assumed to be an ID and the corresponding matrix element is returned that represents the dissimilarity between the two IDs. Note that the order of lookup by ID pair matters if the matrix is asymmetric: the first ID will be used to look up the row, and the second ID will be used to look up the column. Thus, `dm['a', 'b']` may not be the same as `dm['b', 'a']` if the matrix is asymmetric.

  Otherwise, index will be passed through to `DissimilarityMatrix.data.__getitem__`, allowing for standard indexing of a `numpy.ndarray` (e.g., slicing).

  Returns: | Indexed data, where return type depends on the form of index (see description of index for more details).
  Return type: | ndarray or scalar
  Raises: | `MissingIDError` – If the ID(s) specified in index are not in the dissimilarity matrix.

  Notes

  The lookup based on ID(s) is quick.