Hi,
Two thoughts I'd like to share on this subject:
1) Something really cool for conversions between units is the Google
search bar: type in " 3 inches in cm" and you get,
3 inches = 7.62 centimeters
or, " 3 £ in dollar",
3 UK£ = 4.4007 U.S. dollars
or "12 cubic meters to pints",
12 (cubic meters) = 21 117.0391 Imperial pints
That is a very clever pattern recognition, and very useful for this
task.
I think a similar implementation would be great to facilitate the use
of units within R, I'm not sure Google has shared the code though.
2) the Grid package provides the unit() functions that handles
conversions between different systems (inches, cm, pts, ...). I'm sure
Paul Murrell thought a lot about the best implementation for this (I'm
guessing he is the author of that function),
getAnywhere(valid.unit)
function (x, units, data)
{
valid.units <- valid.units(units)
data <- valid.data(rep(units, length.out = length(x)), data)
attr(x, "unit") <- units
attr(x, "valid.unit") <- valid.units
attr(x, "data") <- data
class(x) <- "unit"
x
}
so we could imagine these two functions,
convert(12, from= "m^3", to = "pint", round=FALSE)
or,
unit(12, "m^3") + unit(3, "pint")
Note that lengths (perhaps also time and color to a minor extent) are
especially important in that it's the only actual physical dimension
rendered in a final plot, the others are put in correspondence
(isomorphism between continuous variables) with the labels set
accordingly.
Best wishes,
baptiste
On 13 Apr 2009, at 01:00, Tom La Bone wrote:
Back in 2005 I had been doing most of my work in Mathcad for over 10
years.
For a number of reasons I decided to switch over to R. After much
effort and
help from you folks I am finally "thinking" in R rather than
thinking in
Mathcad and trying to translating to R. Anyway, the only task I
still use
Mathcad for is calculations that involve physical quantities and
units. For
example, in Mathcad I can add 1 kilometer to 1 mile and get the
right answer
in the units of length I choose. Likewise, if I try to add 1
kilometer to 1
kilogram I get properly chastised. Is there a way in R to assign
quantities
and units to numbers and have R keep track of them like Mathcad does?
Tom
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_____________________________
Baptiste Auguié
School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK
Phone: +44 1392 264187
http://newton.ex.ac.uk/research/emag
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
