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#### 3.1.2 Missing Data

It is possible to represent missing data explicitly in Octave using `NA` (short for “Not Available”). Missing data can only be represented when data is represented as floating point numbers. In this case missing data is represented as a special case of the representation of `NaN`.

— Built-in Function: NA (x)
— Built-in Function: NA (n, m)
— Built-in Function: NA (n, m, k, ...)
— Built-in Function: NA (..., class)

> Return a matrix or N-dimensional array whose elements are all equal to the special constant used to designate missing values.

— Mapping Function: isna (x)

> Return 1 for elements of x that are NA (missing) values and zero otherwise. For example,

>               isna ([13, Inf, NA, NaN])
>                    => [ 0, 0, 1, 0 ]