[R] unit attribute to list elements

[baptiste Auguié]

On 28 Dec 2007, at 20:06, Gabor Grothendieck wrote:

> Is this what you want?
>

Perfect! Thanks a lot!

>> Lines <- "cel 3.0 m/s
> + Z0 367 ohm
> + eps0 8.9e-12 F/m
> + "
>> Constants.DF <- read.table(textConnection(Lines), as.is = TRUE)
>> Constants <- as.list(Constants.DF[[2]])
>> names(Constants) <- Constants.DF[[1]]
>> for(i in seq_along(Constants)) comment(Constants[[i]]) <-  
>> Constants.DF[i, 3]
>>
>> # get value
>> Constants$Z0
> [1] 367
>> # get comment
>> comment(Constants$Z0)
> [1] "ohm"
>> # add another Constant
>> Constants$e <- 2.7
>> comment(Constants$e) <- "exp"
>
>
> On Dec 28, 2007 2:33 PM, baptiste Auguié <ba208 at exeter.ac.uk> wrote:
>> Hi,
>>
>> I've started my own (first) package, part of which consists in
>> listing common physical constants (Planck's constant, the speed of
>> light in vacuum, etc). I'm wondering what would be a good way of
>> dealing with pairs of value/unit.
>>
>>
>>> constants <- list( cel = 2.99792458e8 , #m/s
>>> Z0 = 376.730313461, #ohm
>>> eps0 = 8.854187817e-12,#F/m
>>> mu0 = 4*pi*1e-7,#N/A^2
>>> G = 6.67428e-11 # m^3 kg-1 s-2
>>> )
>>
>>
>> I thought I could include the unit in the names attribute of each
>> element, as in :
>>
>>> names(constants$cel)<- " speed of light in vacuum [m.s^-1]"
>>
>>
>> Writing this for every element is very redundant... Is there any way
>> to access and set the name of each first level element of the list?
>>
>>> namesFirstLevelElements(constants)<- c(" speed of light in vacuum
>>> [m.s^-1]",
>>> "impedance of vacuum [some unit]",
>>> ...)
>>
>>
>> Quite possibly, I'm completely on the wring track;
>>
>> - maybe such a package already exists
>>
>> - a custom class or structure would be more appropriate? I don't
>> really know how to deal with classes, though, and I'd like to keep
>> the access to the constants' values as direct and generic as  
>> possible.
>>
>> Many thanks in advance,
>>
>> baptiste
>>
>> _____________________________
>>
>> Baptiste Auguié
>>
>> Physics Department
>> University of Exeter
>> Stocker Road,
>> Exeter, Devon,
>> EX4 4QL, UK
>>
>> Phone: +44 1392 264187
>>
>> http://newton.ex.ac.uk/research/emag
>> http://projects.ex.ac.uk/atto
>>
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>>