Mapping parameters
A vector of property values. length(values) should be one greater than
length(breaks) if extend = TRUE, or one less if extend = FALSE.
If TRUE, intervals are closed on the right, i.e. if values are exactly equal to a
break, they go in the lower group. Otherwise, intervals are closed on the left, so equal
values go in the higher group. FALSE by default.
Extend breaks to c(-Inf, breaks, Inf), i.e. include numbers below and above the
outermost breaks. TRUE by default.
If TRUE, NA values in the result will be left unchanged
from their previous values. Otherwise, NA
normally resets to the default.
Logical. Calculate breaks separately within each column?