4.7.7.1.1.2. statsmodels.tools.grouputils.dummy_sparse¶

statsmodels.tools.grouputils.dummy_sparse(groups)[source]¶

create a sparse indicator from a group array with integer labels

Parameters:

groups: ndarray, int, 1d (nobs,)

an array of group indicators for each observation. Group levels are assumed to be defined as consecutive integers, i.e. range(n_groups) where n_groups is the number of group levels. A group level with no observations for it will still produce a column of zeros.

Returns:

indi : ndarray, int8, 2d (nobs, n_groups)

an indicator array with one row per observation, that has 1 in the column of the group level for that observation

Examples

>>> g = np.array([0, 0, 2, 1, 1, 2, 0])
>>> indi = dummy_sparse(g)
>>> indi
<7x3 sparse matrix of type '<type 'numpy.int8'>'
    with 7 stored elements in Compressed Sparse Row format>
>>> indi.todense()
matrix([[1, 0, 0],
        [1, 0, 0],
        [0, 0, 1],
        [0, 1, 0],
        [0, 1, 0],
        [0, 0, 1],
        [1, 0, 0]], dtype=int8)

current behavior with missing groups >>> g = np.array([0, 0, 2, 0, 2, 0]) >>> indi = dummy_sparse(g) >>> indi.todense() matrix([[1, 0, 0],

[1, 0, 0], [0, 0, 1], [1, 0, 0], [0, 0, 1], [1, 0, 0]], dtype=int8)