[R] degree-min-sec data
Peter Dalgaard
p.dalgaard at biostat.ku.dk
Fri Jan 9 23:41:51 CET 2004
George_Heine at blm.gov writes:
> Hello -
>
> Have both astronomic and geodetic data sets with values in the form
> "ddd:mm:ss.sssss", where dd is an integer between -180 and 180, mm is an
> integer between 0 and 60, and ss is a floating-point
> number between 0 and 60.0. In order to do anything useful with these
> values they need to be turned into their "decimal degree" equivalent.
>
> Assuming the data is a vector y, the following works, sort of:
>
> z<-strsplit(as.character(y),split=":")
> zz<-sapply(z,as.numeric)
> x<- t(c(1,1/60,1/3600) %*% zz)
>
> Trouble comes if there are any NA's in the data. In this case, R refuses
> to coerce zz into matrix form, but leaves it as a "list of lists". How can
> the above routine be patched up to pass NAs through?
> I can think of some inelegant solutions (e.g. recoding NA as "-200:-1:-1")
> but surely there is a better way!
> Or is this the wrong technique?
Not necessarily. I might try something like
z <- strsplit(ifelse(is.na(y),y,"::NA"))
..etc..
There are also fancier possibilities:
z <- scan(textConnection(y),sep=":",fill=TRUE,what=list(a=0,b=0,c=0))
x <- z$a + z$b/60 + z$c/3600
or even
x <- with(z, a + b/60 + c/3600)
> More generally, is there a way to "unzip" a character vector along some
> split marker, handling irregulatirites gracefully? For example, from
>
> y<-c("aaa#bbb", "ccc#ddd", "eee","fff"),
>
> strsplit(y,split="#") would produce
>
> c(c("aaa","bbb"), c("ccc","ddd"), c("eee","fff")).
>
> Is there a way to produce instead
>
> c(c("aaa","ccc","eee"),c("bbb","ddd","fff")) ?
?? Was that what you intended to write?
> dput(strsplit(y,split="#"))
list(c("aaa", "bbb"), c("ccc", "ddd"), "eee", "fff")
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907
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