[GRASS-dev] [GRASS GIS] #3192: add a coalesce function to r.mapcalc

[GRASS GIS]

#3192: add a coalesce function to r.mapcalc
-------------------------+-------------------------------------------------
  Reporter:  aroche      |      Owner:  grass-dev@…
      Type:              |     Status:  new
  enhancement            |
  Priority:  normal      |  Milestone:  7.4.0
 Component:  Raster      |    Version:  unspecified
Resolution:              |   Keywords:  r.mapcalc, coalesce, isnull,
       CPU:              |  r.patch
  Unspecified            |   Platform:  Unspecified
-------------------------+-------------------------------------------------
Changes (by wenzeslaus):

 * keywords:   => r.mapcalc, coalesce, isnull, r.patch
 * component:  Default => Raster
 * milestone:  7.0.6 => 7.4.0


Comment:

 Workaround: The same functionality is available through G7:r.patch.

 [https://www.postgresql.org/docs/9.5/static/functions-conditional.html
 PostgreSQL definition] of function ''COALESCE(value [, ...]'')

 > The COALESCE function returns the first of its arguments that is not
 null. Null is returned only if all arguments are null. It is often used to
 substitute a default value for null values when data is retrieved for
 display, for example:
 >
 > {{{
 > SELECT COALESCE(description, short_description, '(none)') ...
 > }}}
 >
 > This returns description if it is not null, otherwise short_description
 if it is not null, otherwise (none).
 >
 > Like a CASE expression, COALESCE only evaluates the arguments that are
 needed to determine the result; that is, arguments to the right of the
 first non-null argument are not evaluated. This SQL-standard function
 provides capabilities similar to NVL and IFNULL, which are used in some
 other database systems.

 [https://sqlite.org/lang_corefunc.html#coalesce SQLite definition] of
 function ''coalesce(X,Y,...)'':

 > The coalesce() function returns a copy of its first non-NULL argument,
 or NULL if all arguments are NULL. Coalesce() must have at least 2
 arguments.

 [https://sqlite.org/lang_corefunc.html#ifnull SQLite definition] of a
 similar function ''ifnull(X,Y)'':

 > The ifnull() function returns a copy of its first non-NULL argument, or
 NULL if both arguments are NULL. Ifnull() must have exactly 2 arguments.
 The ifnull() function is equivalent to coalesce() with two arguments.

 [https://sqlite.org/lang_corefunc.html#nullif SQLite definition] of a
 function with a similar name ''nullif(X,Y)'':

 > The nullif(X,Y) function returns its first argument if the arguments are
 different and NULL if the arguments are the same.

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Ticket URL: <https://trac.osgeo.org/grass/ticket/3192#comment:1>
GRASS GIS <https://grass.osgeo.org>