These modifiers are used to select specific months from specific
climate parameters, and potentially transform the selections into
their respective sums or means. The modifiers can be chained
together using '+'.
Usage
.range(.months = NULL, .variables = NULL)
.mean(.months = NULL, .variables = NULL)
.sum(.months = NULL, .variables = NULL)
Arguments
.months
numeric identifiers for the months (-1 for previous
January until 12 for current December, with -6 for previous June,
etc.)
.variables
names of the variables the modifier shall be applied to