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 <dwinsem...@comcast.net>
To: David Winsemius <dwinsem...@comcast.net>
Cc: Sadz A <sadz_a1...@yahoo.co.uk>; r-help@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@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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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
