Deepayan Sarkar wrote:
On Wednesday 29 October 2003 09:36, Wolfram Fischer wrote:
How can I divide a unit by an number or average a vector of units, e.g.:
u1 <- unit( 3, 'npc' ) u2 <- unit( 6, 'npc' )
u1 / 2
0.5 * u1
( u1 + u2 ) / 2
0.5 * (u1 + u2)
mean( unit.c(u1,u2) )
Not sure if that's generally doable (other than adding all the units one at a time in a loop and then multiplying by 1/length).
u <- unit.c(u1, u2) 1/unit.length(u) * sum(u)
But if all your units are going to be "npc", you might as well keep the 'x'-s separate and do arithmetic on them.
There are a limited set of mathematical functions/operators for grid units so far.
These include: +, -, and *; sum(), min(), and max().
There are also some unit-specific versions of some other useful functions: unit.c(), unit.rep(), unit.length(), unit.pmin(), unit.pmax()
For more complex calculations involving units, you may need to look at grid.convert() (but take note of the warning on its help page).
Paul -- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 [EMAIL PROTECTED] http://www.stat.auckland.ac.nz/~paul/
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