help working with date values

Gabor,

These options will work just fine. Thank you

Steve

Steve Friedman Ph. D.
Spatial Statistical Analyst
Everglades and Dry Tortugas National Park
950 N Krome Ave (3rd Floor)
Homestead, Florida 33034

Steve_Friedman at nps.gov
Office (305) 224 - 4282
Fax     (305) 224 - 4147


                                                                           
             Gabor                                                         
             Grothendieck                                                  
             <ggrothendieck at gm                                          To 
             ail.com>                  Steve_Friedman at nps.gov              
                                                                        cc 
             04/28/2009 09:39          r-help at r-project.org                
             AM AST                                                Subject 
                                       Re: [R] help working with date      
                                       values                              
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Here are a few ways:

xx <- c("1985-09-02", "1985-09-16", "1985-07-31", "1985-07-31",

"1985-09-02",
"1985-08-26", "1985-07-31", "1985-08-26", "1985-09-02", "1985-09-16")

# 1
library(zoo)
as.numeric(floor(as.yearmon(xx)))

[1] 1985 1985 1985 1985 1985 1985 1985 1985 1985 1985

#2
as.numeric(substr(xx, 1, 4))

[1] 1985 1985 1985 1985 1985 1985 1985 1985 1985 1985

#3
as.numeric(format(as.Date(xx), "%Y"))

[1] 1985 1985 1985 1985 1985 1985 1985 1985 1985 1985

My data contains a variable "observation_date" ?and it contains values

as:

1985-09-02
1985-09-15
1985-07-31
1985-09-02


I need to process data annually rather than daily, therefore I'm trying

to

1) either extract the first 4 digits from this field and use them as a

new

variable "year" ?or 2) keep the variable as it is and process the

analysis

using the first 4 digits of the observation_date field.

I'm not sure how to do either one of these approaches. I've looked in the
R-archive help pages, date, strsplit and a few others

attach(gator)
observation_date[1:10]

?[1] 1985-09-02 1985-09-16 1985-07-31 1985-07-31 1985-09-02 1985-08-26
1985-07-31 1985-08-26 1985-09-02 1985-09-16

as.date(observation_date)

Error in as.date(observation_date) ?: Cannot coerce to date format

mode(observation_date)

?"numeric"

y <- as.character(observation_date)

[1] ?"1985-09-02" "1985-09-16" "1985-07-31" "1985-07-31" "1985-09-02"
"1985-08-26" "1985-07-31" "1985-08-26" "1985-09-02" "1985-09-16"

< y.date <- as.date(y)
?[1] <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> ?on and

on

and on ...

x <- strsplit(observation_date, "-")

Error in strsplit(observation_date, "-") ?: non-character argument


All help is greatly appreciated.

Thanks
Steve



Steve Friedman Ph. D.
Spatial Statistical Analyst
Everglades and Dry Tortugas National Park
950 N Krome Ave (3rd Floor)
Homestead, Florida 33034

Steve_Friedman at nps.gov
Office (305) 224 - 4282
Fax ? ? (305) 224 - 4147

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