R help - Feb 2010 - Convert a column of numbers to a column of strings

Hello,

Please excuse me if this question has been asked before. I'm new to R, and
have been trying to google the answers without any success.

I would like to convert a set of date and time into R date-time class. Right
now, the dates and times are in integer format, so I first need to convert
them into string, and then to R date-time using strptime. However, I have a
problem converting them from integer to string:

data:

Date Time
20091209 1200
20091209 1500
20091209 1800
....
20091210 800
20091210 1000
20091210 1600
....

I used:

tempdate=toString(Date)
day=substr(tempdate, 7, 8)
month=substr(tempdate, 5, 6)
year=substr(tempdate, 1, 2)
rDate=strptime(paste(year, month, day, sep="-"))

the 1st command does not create a new column with string dates in it, it
creates a single row that has all the dates in a single string, like this:
"20091209, 20091209, .... 20091210, 20091210"
"day" ends up being 1 number, 09, instead of a column of days. I ended
up
having all rDate=2009/12/09, which is the first row.

Could you please tell me how to do this correctly?

Thanks,
Tam


-- 


Tam T. Le [MEDS 2001 Sheridan Rd, Evanston IL 60208] [847 708 2439]

	[[alternative HTML version deleted]]

Hello,

Tam Le wrote:
> Hello,
> 
> Please excuse me if this question has been asked before. I'm new to R,
and
> have been trying to google the answers without any success.
> 
> I would like to convert a set of date and time into R date-time class.
Right
> now, the dates and times are in integer format, so I first need to convert
> them into string, and then to R date-time using strptime. However, I have a
> problem converting them from integer to string:
> 
> data:
> 
> Date Time
> 20091209 1200
> 20091209 1500
> 20091209 1800
> ....
> 20091210 800
> 20091210 1000
> 20091210 1600
> ....
> 
> I used:
> 
> tempdate=toString(Date)
> day=substr(tempdate, 7, 8)
> month=substr(tempdate, 5, 6)
> year=substr(tempdate, 1, 2)
> rDate=strptime(paste(year, month, day, sep="-"))
> 
> the 1st command does not create a new column with string dates in it, it
> creates a single row that has all the dates in a single string, like this:
> "20091209, 20091209, .... 20091210, 20091210"
> "day" ends up being 1 number, 09, instead of a column of days. I
ended up
> having all rDate=2009/12/09, which is the first row.
> 
> Could you please tell me how to do this correctly?
#sample data.frame
tmp <- data.frame(Date = c("20091209", "20091209"), Time
=  c("1200",
"1500"))

#Convert, see ?strptime and ?as.POSIXct format argument
as.POSIXct(paste(tmp$Date, tmp$Time), format = "%Y%m%d %H%M")

Also, although you don't need it to accomplish what you want, you were 
probably looking for the as.character function instead of toString...

Tam Le wrote:
> Hello,
> 
> Please excuse me if this question has been asked before. I'm new to R,
and
> have been trying to google the answers without any success.
> 
> I would like to convert a set of date and time into R date-time class.
Right
> now, the dates and times are in integer format, so I first need to convert
> them into string, and then to R date-time using strptime. However, I have a
> problem converting them from integer to string:
> 
> data:
> 
> Date Time
> 20091209 1200
> 20091209 1500
> 20091209 1800
> ....
> 20091210 800
> 20091210 1000
> 20091210 1600
> ....
> 
> I used:
> 
> tempdate=toString(Date)
> day=substr(tempdate, 7, 8)
> month=substr(tempdate, 5, 6)
> year=substr(tempdate, 1, 2)
> rDate=strptime(paste(year, month, day, sep="-"))
> 
> the 1st command does not create a new column with string dates in it, it
> creates a single row that has all the dates in a single string, like this:
> "20091209, 20091209, .... 20091210, 20091210"
> "day" ends up being 1 number, 09, instead of a column of days. I
ended up
> having all rDate=2009/12/09, which is the first row.
> 
> Could you please tell me how to do this correctly?
> 
> Thanks,
> Tam
> 
>

Try this
> Lines <- "Date Time Data
+ 20091209 1200 1
+ 20091209 1500 2
+ 20091209 1800 3
+ 20091210 800 4
+ 20091210 1000 5
+ 20091210 1600 6"
>
> toChron <- function(x) as.chron(sprintf("%d %04d", x[,1],
x[,2]), "%Y%m%d %H%M")
>
> DF <- read.table(textConnection(Lines), header = TRUE)
> toChron(DF)
[1] (12/09/09 12:00:00) (12/09/09 15:00:00) (12/09/09 18:00:00)
(12/10/09 08:00:00) (12/10/09 10:00:00) (12/10/09 16:00:00)

Or if the read problem is to read in a time series try read.zoo in the
zoo package.  The development version of read.zoo supports
multi-column indexes:
>
> library(zoo)
> # grab development version of read.zoo
>
source("http://r-forge.r-project.org/plugins/scmsvn/viewcvs.php/*checkout*/pkg/zoo/R/read.zoo.R?rev=611&root=zoo")
> z <- read.zoo(textConnection(Lines), header = TRUE, index = 1:2, FUN =
toChron); z
(12/09/09 12:00:00) (12/09/09 15:00:00) (12/09/09 18:00:00) (12/10/09
08:00:00) (12/10/09 10:00:00) (12/10/09 16:00:00)
                  1                   2                   3
       4                   5                   6

For more info on dates and times see the article in R News 4/1.  For
more info on zoo see the 3 vignettes (pdf documents) that come with
the package.


On Mon, Feb 1, 2010 at 1:52 PM, Tam Le <lettam at gmail.com>
wrote:
> Hello,
>
> Please excuse me if this question has been asked before. I'm new to R,
and
> have been trying to google the answers without any success.
>
> I would like to convert a set of date and time into R date-time class.
Right
> now, the dates and times are in integer format, so I first need to convert
> them into string, and then to R date-time using strptime. However, I have a
> problem converting them from integer to string:
>
> data:
>
> Date Time
> 20091209 1200
> 20091209 1500
> 20091209 1800
> ....
> 20091210 800
> 20091210 1000
> 20091210 1600
> ....
>
> I used:
>
> tempdate=toString(Date)
> day=substr(tempdate, 7, 8)
> month=substr(tempdate, 5, 6)
> year=substr(tempdate, 1, 2)
> rDate=strptime(paste(year, month, day, sep="-"))
>
> the 1st command does not create a new column with string dates in it, it
> creates a single row that has all the dates in a single string, like this:
> "20091209, 20091209, .... 20091210, 20091210"
> "day" ends up being 1 number, 09, instead of a column of days. I
ended up
> having all rDate=2009/12/09, which is the first row.
>
> Could you please tell me how to do this correctly?
>
> Thanks,
> Tam
>
>
> --
>
>
> Tam T. Le [MEDS 2001 Sheridan Rd, Evanston IL 60208] [847 708 2439]
>
> ? ? ? ?[[alternative HTML version deleted]]
>
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