missex
==============================================

Purpose
----------------

Converts numeric values to the missing value code according to the values given in a logical
expression.

Format
----------------
.. function:: y = missex(x, mask)

    :param x: data
    :type x: NxK matrix

    :param mask: (matrix of 0's and 1's) that serves as a "mask" for *x*; the 1's in
        mask correspond to the values in *x* that are to be converted into missing values
    :type mask: NxK logical matrix

    :return y: but with those elements that correspond to the 1's in *e* converted to missing.

    :rtype y: NxK matrix that equals x

Examples
----------------

Replace negative prices with a missing value
+++++++++++++++++++++++++++++++++++++++++++++++++

::

    prices = { 1.25,
               0.75,
               2.25,
              -1.50,
               2.05 };

    // replace elements below zero
    // with a missing value
    prices = missex(prices, prices .< 0);

::

    1.25 
    0.75 
    2.25 
       . 
    2.05


Replace 

::

    x = { 0.525 0.419,
          0.869 0.973,
          0.021 0.357 };

    // Logical expression
    mask = (x .> .30) .and (x .< .60);
    y = missex(x, mask);

After the code above:

::

              1  1           .      .
       mask = 0  0   y = 0.869  0.973
              0  1       0.021      .


A 3x2 matrix of uniform random numbers is created.
All values in the interval (0.30, 0.60) are converted
to missing.

Remarks
-------

The matrix *e* will usually be created by a logical expression. For
instance, to convert all numbers between 10 and 15 in *x* to missing, the
following code could be used:

::

    y = missex(x, (x .> 10) .and (x .< 15));

Note that "dot" operators MUST be used in constructing the logical
expressions.

For complex matrices, the missing value code is defined as a missing
value entry in the real part of the matrix. For complex *x*, then, :func:`missex`
replaces elements with a ". + 0i" value.

This function is like :func:`miss`, but is more general in that a range of
values can be converted into missings.

Source
------

datatran.src

.. seealso:: Functions :func:`miss`, :func:`missrv`, :func:`where`