# numpy.ma.diag

ma.diag(v, k=0)

  Extract a diagonal or construct a diagonal array.

  This function is the equivalent of `numpy.diag` that takes masked values into account, see `numpy.diag` for details.

  See also

  `numpy.diag`

    Equivalent function for ndarrays.

  Examples

  Create an array with negative values masked:

      >>> import numpy as np
      >>> x = np.array([[11.2, -3.973, 18], [0.801, -1.41, 12], [7, 33, -12]])
      >>> masked_x = np.ma.masked_array(x, mask=x < 0)
      >>> masked_x
      masked_array(
        data=[[11.2, --, 18.0],
              [0.801, --, 12.0],
              [7.0, 33.0, --]],
        mask=[[False,  True, False],
              [False,  True, False],
              [False, False,  True]],
        fill_value=1e+20)

  Isolate the main diagonal from the masked array:

      >>> np.ma.diag(masked_x)
      masked_array(data=[11.2, --, --],
                   mask=[False,  True,  True],
             fill_value=1e+20)

  Isolate the first diagonal below the main diagonal:

      >>> np.ma.diag(masked_x, -1)
      masked_array(data=[0.801, 33.0],
                   mask=[False, False],
             fill_value=1e+20)