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Ko-Kang Kevin Wang

2003-Nov-26 00:23 UTC

[R] strptime Usage

Hi,

I have a column in a dataframe in the form of:> as.vector(SLDATX[1:20]) [1] "1/6/1986"  "1/17/1986" "2/2/1986" 
"2/4/1986"  "2/4/1986"
 [6] "2/21/1986" "3/6/1986"  "3/25/1986"
"4/6/1986"  "4/10/1986"
[11] "4/23/1986" "4/30/1986" "5/8/1986" 
"5/29/1986" "6/15/1986"
[16] "6/18/1986" "6/23/1986" "6/29/1986"
"7/16/1986" "7/25/1986"

I'd like to convert it into either yyyy-mm or yyyy/mm form, e.g. 1986-06 
or 1986/06, and I've been suggsted to use the strptime() function.  

However when I look at the documentation of it and tried something
like:> strptime(as.vector(SLDATX)[1:20], "%y/%m") [1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA

I got a bunch of NA's.  I also tried:> strptime(as.vector(SLDATX)[1:20], "%y/%m/%d") [1] "2001-06-19" NA           "2002-02-19"
"2002-04-19" "2002-04-19"
 [6] NA           "2003-06-19" NA           "2004-06-19"
"2004-10-19"
[11] NA           NA           "2005-08-19" NA           NA
[16] NA           NA           NA           NA           NA

It is totally messed up.

I'd really appreciate if anyone can point out where I did wrong *_*!

Many thanks in advance.


-- 
Cheers,

Kevin

---------------------------------------------------------------
"Try not.  Do, do!  Or do not.  There is no try"
   Jedi Master Yoda

----
Ko-Kang Kevin Wang
Master of Science (MSc) Student
SLC Tutor and Lab Demonstrator
Department of Statistics
University of Auckland
New Zealand
Homepage: http://www.stat.auckland.ac.nz/~kwan022
Ph: 373-7599
    x88475 (City)
    x88480 (Tamaki)

Jason Turner

2003-Nov-26 00:36 UTC

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[R] strptime Usage

Ko-Kang Kevin Wang wrote:
> Hi,
> 
> I have a column in a dataframe in the form of:
> 
>>as.vector(SLDATX[1:20])
> 
>  [1] "1/6/1986"  "1/17/1986" "2/2/1986" 
"2/4/1986"  "2/4/1986"
>  [6] "2/21/1986" "3/6/1986"  "3/25/1986"
"4/6/1986"  "4/10/1986"
> [11] "4/23/1986" "4/30/1986" "5/8/1986" 
"5/29/1986" "6/15/1986"
> [16] "6/18/1986" "6/23/1986" "6/29/1986"
"7/16/1986" "7/25/1986"
> ...

First, you have to make this character vector into a time object.
You want something like:

times <- strptime(as.vector(SLDATX[1:20]),"%d/%m/%Y")

so R knows what format you're using for dates.

 From there, format(times,"%Y/%m") will work.

Subtle trap - strptime produces a list of 9 vectors; "times" will
always
have length 9.  If you want to include this into a data frame, you'll 
need to convert to a  POSIX time type:

as.POSIXct(times)

to get the right length.

Cheers

Jason
-- 
Indigo Industrial Controls Ltd.
http://www.indigoindustrial.co.nz
64-21-343-545
jasont at indigoindustrial.co.nz

Gabor Grothendieck

2003-Nov-26 05:34 UTC

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[R] strptime Usage

strptime takes a character input and produces a POSIXlt output so
the format you specify to strptime is the format of the input, 
not the output:

   format( strptime("10/22/1986", "%m/%d/%Y"),
"%Y-%m" )

---
Date: Wed, 26 Nov 2003 13:23:45 +1300 (NZDT) 
From: Ko-Kang Kevin Wang <kwan022 at stat.auckland.ac.nz>
To: R Help <r-help at stat.math.ethz.ch> 
Subject: [R] strptime Usage 

 
 
Hi,

I have a column in a dataframe in the form of:> as.vector(SLDATX[1:20])[1] "1/6/1986" "1/17/1986" "2/2/1986"
"2/4/1986" "2/4/1986"
[6] "2/21/1986" "3/6/1986" "3/25/1986"
"4/6/1986" "4/10/1986"
[11] "4/23/1986" "4/30/1986" "5/8/1986"
"5/29/1986" "6/15/1986"
[16] "6/18/1986" "6/23/1986" "6/29/1986"
"7/16/1986" "7/25/1986"

I'd like to convert it into either yyyy-mm or yyyy/mm form, e.g. 1986-06 
or 1986/06, and I've been suggsted to use the strptime() function. 

However when I look at the documentation of it and tried something
like:> strptime(as.vector(SLDATX)[1:20], "%y/%m")[1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA

I got a bunch of NA's. I also tried:> strptime(as.vector(SLDATX)[1:20], "%y/%m/%d")[1] "2001-06-19" NA "2002-02-19" "2002-04-19"
"2002-04-19"
[6] NA "2003-06-19" NA "2004-06-19" "2004-10-19"
[11] NA NA "2005-08-19" NA NA
[16] NA NA NA NA NA

It is totally messed up.

I'd really appreciate if anyone can point out where I did wrong *_*!

Many thanks in advance.


-- 
Cheers,

Kevin

---------------------------------------------------------------
"Try not. Do, do! Or do not. There is no try"
Jedi Master Yoda

----
Ko-Kang Kevin Wang
Master of Science (MSc) Student
SLC Tutor and Lab Demonstrator
Department of Statistics
University of Auckland
New Zealand
Homepage: http://www.stat.auckland.ac.nz/~kwan022
Ph: 373-7599
x88475 (City)
x88480 (Tamaki)

______________________________________________
R-help at stat.math.ethz.ch mailing list
https://www.stat.math.ethz.ch/mailman/listinfo/r-help

Ko-Kang Kevin Wang

2003-Dec-01 06:23 UTC

head link

[R] strptime Usage

Thanks!

On Wed, 26 Nov 2003, Gabor Grothendieck wrote:
> Date: Wed, 26 Nov 2003 00:34:11 -0500 (EST)
> From: Gabor Grothendieck <ggrothendieck at myway.com>
> To: kwan022 at stat.auckland.ac.nz, r-help at stat.math.ethz.ch
> Subject: RE: [R] strptime Usage
> 
> 
> 
> strptime takes a character input and produces a POSIXlt output so
> the format you specify to strptime is the format of the input, 
> not the output:
> 
>    format( strptime("10/22/1986", "%m/%d/%Y"),
"%Y-%m" )
It worked perfect.  Just out of interest, if I want to convert (either 
from the original form, i.e. mm/dd/yyyy, or the yyyy-mm form, to quarterly 
format, e.g.:
  1999-1
  1999-2
  1999-3
  1999-4
is it possible to do with strptime?  Or do I have to do something 
creative? ;-D

-- 
Cheers,

Kevin

---------------------------------------------------------------
"Try not.  Do, do!  Or do not.  There is no try"
   Jedi Master Yoda

----
Ko-Kang Kevin Wang
Master of Science (MSc) Student
SLC Tutor and Lab Demonstrator
Department of Statistics
University of Auckland
New Zealand
Homepage: http://www.stat.auckland.ac.nz/~kwan022
Ph: 373-7599
    x88475 (City)
    x88480 (Tamaki)

Prof Brian Ripley

2003-Dec-01 07:45 UTC

head link

[R] strptime Usage

On Mon, 1 Dec 2003, Ko-Kang Kevin Wang wrote:
> Thanks!
> 
> On Wed, 26 Nov 2003, Gabor Grothendieck wrote:
> 
> > Date: Wed, 26 Nov 2003 00:34:11 -0500 (EST)
> > From: Gabor Grothendieck <ggrothendieck at myway.com>
> > To: kwan022 at stat.auckland.ac.nz, r-help at stat.math.ethz.ch
> > Subject: RE: [R] strptime Usage
> > 
> > 
> > 
> > strptime takes a character input and produces a POSIXlt output so
> > the format you specify to strptime is the format of the input, 
> > not the output:
> > 
> >    format( strptime("10/22/1986", "%m/%d/%Y"),
"%Y-%m" )
> 
> It worked perfect.  Just out of interest, if I want to convert (either 
> from the original form, i.e. mm/dd/yyyy, or the yyyy-mm form, to quarterly 
> format, e.g.:
>   1999-1
>   1999-2
>   1999-3
>   1999-4
> is it possible to do with strptime?  Or do I have to do something 
> creative? ;-D
Well, strptime converts from strings to internal date format, so it is 
logically impossible to do this with strptime.

As for quarters: how do you define them?  Does the quarters() function do 
what you want?  If almost, look at
> quarters.POSIXtfunction (x, ...)
{
    x <- (as.POSIXlt(x)$mon)%/%3
    paste("Q", x + 1, sep = "")
}

for ideas.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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