[R] Strptime/ date time classes

jim holtman jholtman at gmail.com
Wed Jul 9 20:45:01 CEST 2008 

Even using POSIXlt it seems to work fine when you are looking for NAs
in the dates (ones that did not convert correctly.  So you must be
doing something different or your data is different from the example
you have in the mail.  You are always requested to provide commented,
minimal, self-contained, reproducible code.

> x <- read.table(textConnection("#TZUTC+0|*|SANR08002|*|SNAMENAUL|*|SWATERDELVIN|*|CNR98808|*|
+ #CNAMEQ|*|CTYPEn-min-ip|*|CMW1440|*|RTIMELVLhigh-resolution|*|
+ #CUNITm3/s|*|RINVAL-777|*|RNR-1|*|REXCHANGE98913|*|
+ #RTYPEinstantaneous values|*|
+ 19800604062759 -777.0
+ 19800604062800 0.271
+ 19800604111900 0.286
+ 19800604134300 0.362
+ 19800604144400 0.465
+ 19800604163300 0.510
+ 19800604175400 0.518
+ 19800604185100 0.526
+ 0611110900 -777.0
+ 19800611110959 -777.0
+ 19800611111000 0.100
+ 19800611211400 0.096
+ 19800612000000 0.096
+ 19800612065000 0.098
+ 19800612133400 0.100"),colClasses=c('character','numeric'))
> closeAllConnections()
> # you probably want POSIXct not POSIXlt
> datetimes <- (strptime(x[,1], "%Y%m%d%H%M%S"))
> str(datetimes)
 POSIXlt[1:9], format: "1980-06-04 06:27:59" "1980-06-04 06:28:00"
"1980-06-04 11:19:00" ...
> length(datetimes)
[1] 9
> a <- (1:15)[is.na(datetimes)]
> datetimes[a]
[1] NA


On Wed, Jul 9, 2008 at 1:18 PM, Caroline Keef
<caroline.keef at jbaconsulting.co.uk> wrote:
> Thank you, but why does this happen?
>
> a =(1:223960)[is.na(datetimes)]
> datetimes[a]
>>  [1] "1981-03-29 01:20:00" "1990-03-25 01:43:00" "1992-03-29 01:43:00"
>
>> "1996-03-31 01:30:00" "1996-03-31 01:57:00"  [6] "1997-03-30 01:02:00"
>
>> "1997-03-30 01:14:00" "1997-03-30 01:27:00" "1997-03-30 01:44:00"
>> "1997-03-30 01:55:00" [11] "1998-03-29 01:16:00" "1998-03-29 01:41:00"
>
>> "1998-03-29 01:56:00" "1999-03-28 01:03:00" "1999-03-28 01:18:00" [16]
>
>> "2000-03-26 01:28:00"
>
> Which obviously aren't missing.
>
> I do want POSIXlt as I need to extract the day of the month (I'm
> extracting daily maxima from irregulrly observed time series).
>
> This seems like a bug to me, I just thought I'd check with people who
> know more than I do.
>
> Caroline
>
>
> -----Original Message-----
> From: jim holtman [mailto:jholtman at gmail.com]
> Sent: 09 July 2008 17:24
> To: Caroline Keef
> Cc: r-help at r-project.org
> Subject: Re: [R] Strptime/ date time classes
>
>
> You probably want POSIXct instead of POSIXlt:
>
>  x <-
> read.table(textConnection("#TZUTC+0|*|SANR08002|*|SNAMENAUL|*|SWATERDELV
> IN|*|CNR98808|*|
> + #CNAMEQ|*|CTYPEn-min-ip|*|CMW1440|*|RTIMELVLhigh-resolution|*|
> + #CUNITm3/s|*|RINVAL-777|*|RNR-1|*|REXCHANGE98913|*|
> + #RTYPEinstantaneous values|*|
> + 19800604062759 -777.0
> + 19800604062800 0.271
> + 19800604111900 0.286
> + 19800604134300 0.362
> + 19800604144400 0.465
> + 19800604163300 0.510
> + 19800604175400 0.518
> + 19800604185100 0.526
> + 19800611110900 -777.0
> + 19800611110959 -777.0
> + 19800611111000 0.100
> + 19800611211400 0.096
> + 19800612000000 0.096
> + 19800612065000 0.098
> + 19800612133400 0.100"),colClasses=c('character','numeric'))
>> closeAllConnections()
>> # you probably want POSIXct not POSIXlt
>> datetimes <- as.POSIXct(strptime(x[,1], "%Y%m%d%H%M%S"))
>> str(datetimes)
>  POSIXct[1:15], format: "1980-06-04 06:27:59" "1980-06-04 06:28:00"
> "1980-06-04 11:19:00" ...
>> length(datetimes)
> [1] 15
>>
>
>
> On Wed, Jul 9, 2008 at 6:09 AM, Caroline Keef
> <caroline.keef at jbaconsulting.co.uk> wrote:
>> Dear all,
>>
>> I've come across a problem using strptime, can anyone explain what's
>> going on?  I'm using version 2.7.0 on Windows XP.
>>
>> Thank you
>>
>> Caroline
>>
>> First read in a data file using read.table
>>
>> alldata = read.table(file, header=F, skip=4, colClasses =
>> c("character","numeric"))
>>
>> dim(alldata)
>> [1] 223960      2
>>
>> # inefficient, safe way of sorting out missing or dodgy data
>>
>> alldata[,2][alldata[,2] < 0] = NA
>>
>> # first ten lines of the data
>>
>>  alldata[1:10,]
>>               V1    V2
>> 1  19800604062759    NA
>> 2  19800604062800 0.271
>> 3  19800604111900 0.286
>> 4  19800604134300 0.362
>> 5  19800604144400 0.465
>> 6  19800604163300 0.510
>> 7  19800604175400 0.518
>> 8  19800604185100 0.526
>> 9  19800611110900    NA
>> 10 19800611110959    NA
>>
>> #Then convert the first column using strptime
>>
>> datetimes = strptime(alldata[,1],format="%Y%m%d%H%M%S")
>>
>> #Then I want to get minimum and maximum, but some seem to be missing
>> when they aren't.
>>
>> length(as.POSIXlt(datetimes))  #also equal to length(datetimes)
>>
>> [1] 9
>>
>> # Why isn't this 223960?  Is it something to do with the class?
>>
>> # This is the really puzzling bit (to me anyway)
>>
>> a =(1:223960)[is.na(datetimes)]
>>
>> # which gives
>> 1462  14295  18744  50499  50500  92472  92473  92474  92475  92476
>> 137525 137526 137527 171066 171067 192353
>>
>> # 16 values
>>
>>  alldata[a,]
>>                   V1    V2
>> 1462   19810329012000 0.983
>> 14295  19900325014300 0.219
>> 18744  19920329014300 0.246
>> 50499  19960331013000 0.564
>> 50500  19960331015700 0.563
>> 92472  19970330010200 0.173
>> 92473  19970330011400 0.172
>> 92474  19970330012700 0.172
>> 92475  19970330014400 0.172
>> 92476  19970330015500 0.172
>> 137525 19980329011600 0.427
>> 137526 19980329014100 0.427
>> 137527 19980329015600 0.427
>> 171066 19990328010300 0.223
>> 171067 19990328011800 0.223
>> 192353 20000326012800 0.189
>>
>>  datetimes[a]
>>  [1] "1981-03-29 01:20:00" "1990-03-25 01:43:00" "1992-03-29 01:43:00"
>
>> "1996-03-31 01:30:00" "1996-03-31 01:57:00"  [6] "1997-03-30 01:02:00"
>
>> "1997-03-30 01:14:00" "1997-03-30 01:27:00" "1997-03-30 01:44:00"
>> "1997-03-30 01:55:00" [11] "1998-03-29 01:16:00" "1998-03-29 01:41:00"
>
>> "1998-03-29 01:56:00" "1999-03-28 01:03:00" "1999-03-28 01:18:00" [16]
>
>> "2000-03-26 01:28:00"
>>
>> # They're all around the end of March!  I've looked at the data file
>> and I can't see anything funny in it around these dates.
>>
>>
>>
>> The first few lines of the data file look like
>>
>> #TZUTC+0|*|SANR08002|*|SNAMENAUL|*|SWATERDELVIN|*|CNR98808|*|
>> #CNAMEQ|*|CTYPEn-min-ip|*|CMW1440|*|RTIMELVLhigh-resolution|*|
>> #CUNITm3/s|*|RINVAL-777|*|RNR-1|*|REXCHANGE98913|*|
>> #RTYPEinstantaneous values|*|
>> 19800604062759 -777.0
>> 19800604062800 0.271
>> 19800604111900 0.286
>> 19800604134300 0.362
>> 19800604144400 0.465
>> 19800604163300 0.510
>> 19800604175400 0.518
>> 19800604185100 0.526
>> 19800611110900 -777.0
>> 19800611110959 -777.0
>> 19800611111000 0.100
>> 19800611211400 0.096
>> 19800612000000 0.096
>> 19800612065000 0.098
>> 19800612133400 0.100
>>
>>
>>
>>
>>
>> Caroline KeefJBA Consulting
>> South Barn, Broughton Hall, Skipton, North Yorkshire, BD23 3AE, UK
>> t: +44 (0)1756 799919  f: +44 (0)1756 799449
>>
>> JBA Consulting now incorporates Maslen Environmental, the award
>> winning environmental regeneration consultancy.
>> http://www.maslen-environmental.com.
>>
>> JBA is a Carbon Neutral Company. Please don't print this e-mail unless
>
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>>
>> This email is covered by JBA Consulting's email disclaimer at
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>>
>> ______________________________________________
>> R-help at 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.
>>
>
>
>
> --
> Jim Holtman
> Cincinnati, OH
> +1 513 646 9390
>
> What is the problem you are trying to solve?
>
> ______________________________________________
> R-help at 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.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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