Undefined values: Difference between revisions

2. For variables that are defined for the Julia program but have undefined values, there are two different notionstypes of undefined value in Julia (version > 0.7): <code> nothing </code> and <code> missing </code>. "nothing" and "missing" are typed constants used by convention to refer to either (with <code> nothing </code>) an absent result, such as a search with nothing found, or in the case of <code> missing, </code> a data location containing a missing value, such as a data table with missing values. <code>nothing</code> generally produces an error if any calculations incorporate it, but <code>missing</code> can be propagated along a calculation: