[R] Changing sign on absolute numbers 0 problems
Keith Jewell
k.jewell at campden.co.uk
Thu Oct 21 18:06:17 CEST 2010
In case it helps...
> test <- c("-0:00:53", "-0:01:10.", "-0:01:26.", "-0:01:38.", "-0:01:43",
+ "-0:01:59.", "-0:03:50.", "-0:04:46", "-0:05:01.", "-0:05:16.",
+ "3:41:33.0", "3:43:09.4", "3:44:26.3", "3:47:26.0", "3:48:19.3",
+ "3:52:13.4", "3:57:10.2", "4:29:37.6", "5:01:28.4", "5:08:45.6" )
> require(sp)
> as.numeric.DMS(char2dms(paste(sub("$", '"',sub(":", "'",sub(":", "d",
> test))),ifelse(substring(test,1,1)=="-","W","E"), sep="")))
[1] -0.01472222 -0.01944444 -0.02388889 -0.02722222 -0.02861111 -0.03305556
-0.06388889 -0.07944444 -0.08361111
[10] -0.08777778 3.69250000 3.71927778 3.74063889 3.79055556 3.80536111
3.87038889 3.95283333 4.49377778
[19] 5.02455556 5.14600000
"David Winsemius" <dwinsemius at comcast.net> wrote in message
news:9C5D0D83-2CEB-4F5C-A57E-C75FBBDA9617 at comcast.net...
> With permission I am copying a private communication to the list.
>
> On Oct 21, 2010, at 9:20 AM, Sadz A wrote:
>
>> Hi,
>>
>> I think maybe I did not explain myself properly, I'll try again;
>>
>> I am trying to convert location data in DMS degrees to decimal degrees
>> format.
>>
>> I have attached my data and below is the work I have done so far and
>> notes explaining what I have done. The problem is negative 0, the +/-
>> sign indicates direction so it is very important to have the right sign
>> in front, but R takes 0 and -0 as 0.
>>
>> #approach
>> #download 'gsubfn' from R CRAN.
>>
>> #please insert appropriate directory, the table is attached#
>> data<-read.table("vol by genous lat lon.txt",header=T)
>> names(data)
>> attach(data)
>> library(gsubfn)
>>
>> #the latitude data is in "MD_LATITUD" so to separate out the numbers and
>> convert to decimal degrees i used.......
>
> At this point I realized that my earlier assumption that -0 == 0 might
> not be as "obvious" as I had thought, at least when it applies to the
> leading degrees entry in a latitude, which I was not thinking about very
> clearly.
>>
>> latitude<-as.vector(MD_LATITUD)
>> x <- c(latitude)
>> Convert <- function(d, m, s, dd = as.numeric(d), mm = as.numeric(m), ss
>> = as.numeric(s)) sign(dd) * (abs(dd) + mm / 60 + ss / 3600)
>
> The problem as I saw it was that the as.numeric conversion of d to dd was
> throwing away the sign.
>
> test <- c("-0:00:53", "-0:01:10.", "-0:01:26.", "-0:01:38.", "-0:01:43",
> "-0:01:59.", "-0:03:50.", "-0:04:46", "-0:05:01.", "-0:05:16.",
> "3:41:33.0", "3:43:09.4", "3:44:26.3", "3:47:26.0", "3:48:19.3",
> "3:52:13.4", "3:57:10.2", "4:29:37.6", "5:01:28.4", "5:08:45.6" )
>
> So I substituted an ifelse( grepl(d) -1,1) test for "-" from the
> unconverted degree entry:
>
> Convert <- function(d, m, s, dd = as.numeric(d), mm = as.numeric(m),
> ss = as.numeric(s)){
> ifelse(grepl("-", d),-1,1) * (abs(dd) + mm / 60
> + ss / 3600) }
>
> Lat<-strapply(test, "(.*):(.*):(.*)", Convert, simplify = TRUE)
>
> > Lat
>
> [1] -0.01472222 -0.01944444 -0.02388889 -0.02722222 -0.02861111 -0.03305556
> -0.06388889 -0.07944444
> [9] -0.08361111 -0.08777778 3.69250000 3.71927778 3.74063889
> 3.79055556 3.80536111 3.87038889
> [17] 3.95283333 4.49377778 5.02455556 5.14600000
>
>
>> Lat<-strapply(x, "(.*):(.*):(.*)", Convert, simplify = TRUE)
>> Lat
>>
>> #as you can see in Lat there are lots of 0's, which should not be there
>> but are because 'sign(dd)' takes +ve when +ve, -ve when -ve and
>> multiplies it by 'abs(dd)....' which is correct, BUT for 0 it assigns
>> niether +ve or -ve, giving 0 a 0, and anything times 0 is 0..........
>>
>> #I modified the code to
>>
>> latitude<-as.vector(MD_LATITUD)
>> x <- c(latitude)
>> Convert <- function(d, m, s, dd = as.numeric(d), mm = as.numeric(m), ss
>> = as.numeric(s)) sign(ifelse(dd==0,sign(dd))) * (abs(dd) + mm / 60 + ss
>> / 3600)
>> Lat<-strapply(x, "(.*):(.*):(.*)", Convert, simplify = TRUE)
>> Lat
>>
>> #so I now have the correct absolute decimal degrees in all cases and the
>> correct direction in all cases except where there should be a -0!,
>> because -0's are ignored and assumed to be the same as +0 which is wrong
>> because the + and - indicate direction.
>>
>> # Do you know of a way I can get R to separate out the sign from
>> MD_LATITUD, so that I can change
>> # 'Convert <- function(d, m, s, dd = as.numeric(d), mm = as.numeric(m),
>> ss = as.numeric(s)) sign(dd) * (abs(dd) + mm / 60 + ss / 3600)' to
>> something like
>> # 'Convert <- function(sign, d, m, s, dd = as.numeric(d), mm =
>> as.numeric(m), ss = as.numeric(s)) sign * (abs(dd) + mm / 60 + ss /
>> 3600) #(this does not work but something similar, or a different
>> approach may?)
>>
>> Any help will be appreciated.
>> Thank you
>> sadz
>>
>>
>> From: David Winsemius <dwinsemius at comcast.net>
>> To: David Winsemius <dwinsemius at comcast.net>
>> Cc: Sadz A <sadz_a1000 at yahoo.co.uk>; r-help at r-project.org
>> Sent: Wed, 20 October, 2010 20:45:39
>> Subject: Re: [R] Changing sign on absolute numbers 0 problems
>>
>>
>> On Oct 20, 2010, at 3:19 PM, David Winsemius wrote:
>>
>> >
>> > On Oct 20, 2010, at 11:47 AM, Sadz A wrote:
>> >
>> >> Hi,
>> >>
>> >> I am trying to do some calculations turning DMS data to decimal
>> degrees using
>> >> the formula (D+(M/60)+(S/3600)), some of the D's involve -ve
>> numbers, the
>> >> easiest way to do the calculation is to use absolute numbers then
>> use the 'sign'
>> >> function in R to change the answer back to the correct -ve or +ve,
>> >>
>> >> for example, if;
>> >> D<--69
>> >> M<-8
>> >> S<-10
>> >> then
>> >> decimal<-D+(M/60)+(S/3600)
>> >> -69+(8/60)+(10/3600) = this would equal -68.86389 (which is
>> wrong, it should
>> >> be -69.13611, so i used the following function)
>> >>
>> >> decimal<-(abs(D)+(M/60)+(S/3600))
>> >> decimal.degs<-sign(D)*decimal
>> >> decimal.degs
>> >> -69.13611
>> >>
>> >> because ((69+(8/60)+(10/3600)=69.13611) and then the -sign is put
>> back in.
>> >>
>> >> This works fine untill D=0
>> >> because then 'sign' does not give 0 a +ve sign it takes it as 0
>> and multiplies
>> >> decimal by 0 to give 0.
>> >> example
>> >> D<-0
>> >> decimal<-D+(M/60)+(S/3600)
>> >> decimal.degs<-sign(D)*decimal
>> >> decimal.degs
>> >> 0
>> >>
>> >> Is there anyway to get around this??????????
>> >
>> > I am not sure I understand the source of your distress. Why are
>> you disturbed that 0 returns 0? ??????
>> >
>> >> and make D=0 a positive and not a 0 with sign or another
>> function??????
>> >
>> > You can always define your own function:
>> >
>> > nonneg <- function(x) { 0 + !sign(x) }
>> >
>> > > nonneg(0)
>> > [1] 1
>>
>> Insufficient testing. Try instead:
>>
>> > nonneg <- function(x) { 0+(x >= 0 )}
>> > nonneg(c(-2,-1,0,1,2))
>> [1] 0 0 1 1 1
>>
>>
>> >
>> >
>> >>
>> >> Any help is appreciated
>> >> Thank you
>> >> sadz
>> >>
>> >> ps please email me if you need more info
>> > --David Winsemius, MD
>> > West Hartford, CT
>> >
>> > ______________________________________________
>> > R-help at r-project.org mailing list
>> > https://stat.ethz.ch/mailman/listinfo/r-help
>> > PLEASE do read the posting guide
>> > http://www.R-project.org/posting-guide.html
>> > and provide commented, minimal, self-contained, reproducible code.
>>
>> David Winsemius, MD
>> West Hartford, CT
>>
>>
>> <vol by genous lat lon.txt>
>
> David Winsemius, MD
> West Hartford, CT
>
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