as.unit() ought to use a csv driver file, like rename() does

[dankelley]

Doing that will simplify the code, and also make it a lot easier for users to extend the capabilities of as.unit().

This is in-line with the way rename() works, and how (frankly) things ought to have worked for a long time. I think this can be done without causing problems, but I'll do it in a new branch (named "as_unit") to avoid any problems, since I expect I'll be adding quite a few units, to handle the data that I lately download from IOOS servers.

[dankelley]

The snapshot shows the idea. We need to enclose the first column in quotes, to allow commas in regular expressions. Quotes would also be needed in the 3rd column if the scale contains a comma. I suppose we don't really need quotes in most of those lines, so I might remove them.

Anyway, the code will work a lot like how rename() works, so that users can supply their own unit mappings as files or data frames, or use a built-in mapping.

I won't bother explaining the format more here; the docs will be the place for that.

[dankelley]

Actually, there is no need for anchors (the ^ and $ characters) because we don't have that for the rename() definition files.

[dankelley]

Protection is needed for superscripts, e.g. if we use

kg/m\^3,kg/m^3,

in the file, it can be decoded with (e.g. after reading the file into U):

> U[which(sapply(U[,1], \(p) grepl(paste0("^",p,"$"),"kg/m^3"))),2]
[1] "kg/m^3"
> U[66,]
         V1     V2 V3
66 kg/m\\^3 kg/m^3

[dankelley]

These are the units (as read from the csv file I'm working on) as of now. I'll think this reproduces what I have hard-wired at the moment, but I have not checked yet. My next step will be to give as.unit() a new parameter to read a CSV file like this. (The idea is to keep the old behaviour as a default, and to enable this new behaviour slowly.)

V1	V2	V3
MicroEinstein[s]{0,1} m-2 s-1	mu*Einsten/m^2/s
count[s]{0,1}	count
dbar[s]{0,1}	dbar
decibar[s]{0,1}	dbar
degree[s]{0,1} decimal minutes	degree dec. min.
degree[s]{0,1}	degree
degree[s]{0,1}.C	degree*C
degree[s]{0,1}.celsius	degree*C
degree[s]{0,1}.east	degree*E
degree[s]{0,1}.north	degree*N
degree[s]{0,1}.south	degree*S
degree[s]{0,1}.west	degree*W
degree[s]{0,1}_C	degree*C
degree[s]{0,1}_east	degree*East
degree[s]{0,1}_north	degree*North
pH unit[s]{0,1}	pH
%	%
/m/sr	m^-1*sr^-1
1
1/m	1/m
NTU	NTU
PSS-78	PSS-78
S m-1	S/m
S m^-1	S/m
S/m	S/m
ah	A*hr
amp	A
amp-hrs	A*hr
bar	bar
bool
boolean
byte
cc	cm^3
celsius	degree*C
db	dbar
dbar	dbar
deg	degree
degc	degree*C
degree decimal minutes	degree dec. min.
enum
inHg	inch*Hg
inch	inch
ipts[ -]68	degree*C	IPTS-68
its[ -]90	degree*C	ITS-90
kg m-3	kg/m^3
kg m-3	kg/m^3
kg/m^3	kg/m^3
m s-1	m/s
m s^-2	m/s^2
m	m
m	m
m	m
m-1	1/m
m/s	m/s
m/s^2	m/s^2
mS cm-1	mS/cm
mS cm^-1	mS/cm
mS/cm	mS/cm
mV	mV
mg m-3	mg/m^3
mg m-3	mg/m^3
mg/m^3	mg/m^3
micromol l-1	mu*mol/l
micromol l^-1	mu*mol/l
micromol/l	mu*mol/l
micromole kg-1	mu*mol/kg
micromole kg^-1	mu*mol/kg
micromole/kg	mu*mol/kg
ml [lL]^-1	ml/l
ml [lL]-1	ml/l
ml/[lL]	ml/l
muS cm-1	mu*S/cm
muS cm^-1	mu*S/cm
muS/cm	mu*S/cm
nodim
ppb	ppb
pss-78		PSS-78
psu		PSS-78
rad	rad
s m-1	s/m
s m^-1	s/m
s	s
s/m	s/m
sec	s
seconds since 1970-01-01T00:00:00Z	s	since 1970-01-01
seconds since 1990-01-01	s	since 1990-01-01
uEinsteins s-1 m-2	mu*Einstein/m^2/s^1
uEinsteins s^-1 m^-2	mu*Einstein/m^2/s^1
uEinsteins/s/m^2	mu*Einstein/m^2/s^1
ug/kg	mu*g/kg
ug/l	mu*g/l
umol kg-1	mu*mol/kg
umol l-1	mu*mol/l
umol l^-1	mu*mol/l
umol/kg	mu*mol/kg
umol/l	mu*mol/l
unixtimestamp	s	since 1970-01-01
uw cm^-2 nm^-1	mu*W/cm^2/nm
uw/cm-2 nm-1	mu*W/cm^2/nm
uw/cm^2/nm	mu*W/cm^2/nm
volt	V
volts	V
watt	W
watts	W