R help - Aug 2010 - Converting degree: minute: second data to decimal degree data, should be simple

Hi All, 

I have location data set up as degrees: minutes: seconds (for example, 
122:45:45) I need to get this data into decimal degree form (122.7625). 

I know that I need to use the formula

Decimal degrees = Degrees + (Minutes/60) + (Seconds/3600)

Does anyone know how I can get R to do this?
The original data is all in one column (called 'lat') and the degrees,
mins and
secs are divided by ':'
There are some values that are negative (eg -69:38:27)
I have R version 2.10.1 on a windows vista computer. 

I could do it manually but I have like 20,000 entries and would really like a 
little code to automate the conversion. 

I have tried Microsoft Access and Excel, but because the data is not stored in 
3 columns I cannot get it to work, I figured R was my best option but I cant get
it to work. It should be really simple but I'm new to R so would 
really appreciate help.

 Thank you for reading my plea, 
Any and all help is greatly appreciated,
sadz 



      
	[[alternative HTML version deleted]]

I take it you have the data in character form.  If the DMS data is already in a
data frame it is probably in factor form, so you will need to coerce it to
character first.  Here is how you could do it with the DMS data in a data frame:
> m  ## an example with 3 entries
        DMS
1 122:45:45
2 122:45:45
3 122:45:45
> m <- within(m, {
+ dms <- do.call(rbind, strsplit(as.character(DMS), ":"))
+ dec <- as.numeric(dms[,1]) + 
+   (as.numeric(dms[,2]) + as.numeric(dms[,3])/60)/60
+ rm(dms)
+ })
> m
        DMS      dec
1 122:45:45 122.7625
2 122:45:45 122.7625
3 122:45:45 122.7625
> 
m$dec is thhen the required decimal degrees.

Bill Venables.
 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Sadz A
Sent: Tuesday, 17 August 2010 9:28 AM
To: r-help at r-project.org
Subject: [R] Converting degree: minute: second data to decimal degree data,
should be simple

Hi All, 

I have location data set up as degrees: minutes: seconds (for example, 
122:45:45) I need to get this data into decimal degree form (122.7625). 

I know that I need to use the formula

Decimal degrees = Degrees + (Minutes/60) + (Seconds/3600)

Does anyone know how I can get R to do this?
The original data is all in one column (called 'lat') and the degrees,
mins and
secs are divided by ':'
There are some values that are negative (eg -69:38:27)
I have R version 2.10.1 on a windows vista computer. 

I could do it manually but I have like 20,000 entries and would really like a 
little code to automate the conversion. 

I have tried Microsoft Access and Excel, but because the data is not stored in 
3 columns I cannot get it to work, I figured R was my best option but I cant get
it to work. It should be really simple but I'm new to R so would 
really appreciate help.

 Thank you for reading my plea, 
Any and all help is greatly appreciated,
sadz 



      
	[[alternative HTML version deleted]]

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On Mon, Aug 16, 2010 at 7:27 PM, Sadz A <sadz_a1000 at yahoo.co.uk>
wrote:
> Hi All,
>
> I have location data set up as degrees: minutes: seconds (for example,
> 122:45:45) I need to get this data into decimal degree form (122.7625).
>
> I know that I need to use the formula
>
> Decimal degrees = Degrees + (Minutes/60) + (Seconds/3600)
>
> Does anyone know how I can get R to do this?
> The original data is all in one column (called 'lat') and the
degrees, mins and
> secs are divided by ':'
> There are some values that are negative (eg -69:38:27)
> I have R version 2.10.1 on a windows vista computer.
>
> I could do it manually but I have like 20,000 entries and would really like
a
> little code to automate the conversion.
>
> I have tried Microsoft Access and Excel, but because the data is not stored
in
> 3 columns I cannot get it to work, I figured R was my best option but I
cant get
> it to work. It should be really simple but I'm new to R so would
> really appreciate help.
>
> ?Thank you for reading my plea,
> Any and all help is greatly appreciated,
> sadz
Try this.  strapply matches the indicated regular expression to x
extracting the matches to the parenthesized portions and passing those
matches to separate arguments of f whose output is returned.  Your
formula has been modified slightly here to handle negative numbers.
> library(gsubfn)
> x <- c("122:45:45", "-69:38:27")
> f <- function(d, m, s, dd = as.numeric(d), mm = as.numeric(m), ss =
as.numeric(s)) sign(dd) * (abs(dd) + mm / 60 + ss / 3600)
> strapply(x, "(.*):(.*):(.*)", f, simplify = TRUE)
[1] 122.76250 -69.64083

There is more info on strapply and the gsubfn package at
http://gsubfn.googlecode.com