[R] grid: dividing units by numbers

[Paul Murrell]

Hi


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
paul at stat.auckland.ac.nz
http://www.stat.auckland.ac.nz/~paul/