(octave.info)Missing Data

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3.1.2 Missing Data
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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’.

 -- : NA
 -- : NA (N)
 -- : NA (N, M)
 -- : NA (N, M, K, ...)
 -- : NA (..., CLASS)
     Return a scalar, matrix, or N-dimensional array whose elements are
     all equal to the special constant used to designate missing values.

     Note that NA always compares not equal to NA (NA != NA). To find NA
     values, use the ‘isna’ function.

     When called with no arguments, return a scalar with the value ‘NA’.

     When called with a single argument, return a square matrix with the
     dimension specified.

     When called with more than one scalar argument the first two
     arguments are taken as the number of rows and columns and any
     further arguments specify additional matrix dimensions.

     The optional argument CLASS specifies the return type and may be
     either "double" or "single".

     See also: Note: isna.

 -- : isna (X)
     Return a logical array which is true where the elements of X are NA
     (missing) values and false where they are not.

     For example:

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

     See also: Note: isnan, Note: isinf, Note:
     isfinite.