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Daniel Nordlund

2015-Oct-30 17:35 UTC

[R] how to work with time of day (independent of date)

I have a data frame with date/times represented as charaacter strings 
and and a value at that date/time.  I want to get the mean value for 
each time of day, across days, and then plot time of day on the x-axis 
and means on the y-axis.  R doesn't appear to have a built-in time of 
day time type (independent of a date), unless I have missed something. 
What is the best way to create a time variable so that I can aggregate 
and plot by time of day, with time labelled in HH:MM format.  My current 
approach is to convert all date/times to the same date.  I can then 
manage the rest of what I want with ggplot2.  But I am  wondering if 
there is an easier/better way to do deal with time of day.

Here is a sample data frame.

df <- structure(list(date = structure(1:8, .Label = c("2015-10-29 
00:50:00",
"2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
"2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
"2015-10-31 10:30:00"), class = "factor"), value = c(88L,
17L,
80L, 28L, 23L, 39L, 82L, 79L)), .Names = c("date", "value"),
row.names =
c(NA,
-8L), class = "data.frame")


Any suggestions appreciated.

Dan

-- 
Daniel Nordlund
Bothell, WA  USA

jim holtman

2015-Oct-30 17:56 UTC

head link

[R] how to work with time of day (independent of date)

is this what you want:
> df <- structure(list(date = structure(1:8, .Label = c("2015-10-2900:50:00",
+ "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
+ "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
+ "2015-10-31 10:30:00"), class = "factor"), value = c(88L,
17L,
+ 80L, 28L, 23L, 39L, 82L, 79L)), .Names = c("date",
"value"), row.names c(NA,
+ -8L), class = "data.frame")>
> # extract just the time and summarize by it
> tapply(df$value, substring(df$date, 12, 16), mean)00:50 09:30 10:30 21:10
 66.0  20.0  79.0  59.5



Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

On Fri, Oct 30, 2015 at 1:35 PM, Daniel Nordlund <djnordlund at
frontier.com>
wrote:
> I have a data frame with date/times represented as charaacter strings and
> and a value at that date/time.  I want to get the mean value for each time
> of day, across days, and then plot time of day on the x-axis and means on
> the y-axis.  R doesn't appear to have a built-in time of day time type
> (independent of a date), unless I have missed something. What is the best
> way to create a time variable so that I can aggregate and plot by time of
> day, with time labelled in HH:MM format.  My current approach is to convert
> all date/times to the same date.  I can then manage the rest of what I want
> with ggplot2.  But I am  wondering if there is an easier/better way to do
> deal with time of day.
>
> Here is a sample data frame.
>
> df <- structure(list(date = structure(1:8, .Label = c("2015-10-29
> 00:50:00",
> "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
> "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
> "2015-10-31 10:30:00"), class = "factor"), value =
c(88L, 17L,
> 80L, 28L, 23L, 39L, 82L, 79L)), .Names = c("date",
"value"), row.names > c(NA,
> -8L), class = "data.frame")
>
>
> Any suggestions appreciated.
>
> Dan
>
> --
> Daniel Nordlund
> Bothell, WA  USA
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>
	[[alternative HTML version deleted]]

William Dunlap

2015-Oct-30 18:22 UTC

head link

[R] how to work with time of day (independent of date)

You can use difftime objects to get the amount of time since the start of
the current day.  E.g.,
  > dateTime <- as.POSIXlt( c("2015-10-29 00:50:00",
  + "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
  + "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
  + "2015-10-31 10:30:00"))
  > date <- trunc(dateTime, units="days")
  > sinceMidnight <- difftime(dateTime, date, units="mins")
  > sinceMidnight
  Time differences in mins
  [1]   50  570 1270   50  570 1270   50  630

I use difftime(x, y, units=) instead of the similar x-y because the latter
chooses
the units based on how far apart x and y are, while the former gives me
consistent
units:
  > dateTime[1] - date[1]
  Time difference of 50 mins
  > as.numeric(.Last.value)
  [1] 50
  > dateTime[5:6] - date[5:6]
  Time differences in hours
  [1]  9.50000 21.16667
  > as.numeric(.Last.value)
  [1]  9.50000 21.16667

Depending on what you are using this for, you might want to compute time
since 3am
of the current day so you don't get discontinuities for most times when the
time
changes in spring and fall.



Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Fri, Oct 30, 2015 at 10:35 AM, Daniel Nordlund <djnordlund at
frontier.com>
wrote:
> I have a data frame with date/times represented as charaacter strings and
> and a value at that date/time.  I want to get the mean value for each time
> of day, across days, and then plot time of day on the x-axis and means on
> the y-axis.  R doesn't appear to have a built-in time of day time type
> (independent of a date), unless I have missed something. What is the best
> way to create a time variable so that I can aggregate and plot by time of
> day, with time labelled in HH:MM format.  My current approach is to convert
> all date/times to the same date.  I can then manage the rest of what I want
> with ggplot2.  But I am  wondering if there is an easier/better way to do
> deal with time of day.
>
> Here is a sample data frame.
>
> df <- structure(list(date = structure(1:8, .Label = c("2015-10-29
> 00:50:00",
> "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
> "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
> "2015-10-31 10:30:00"), class = "factor"), value =
c(88L, 17L,
> 80L, 28L, 23L, 39L, 82L, 79L)), .Names = c("date",
"value"), row.names > c(NA,
> -8L), class = "data.frame")
>
>
> Any suggestions appreciated.
>
> Dan
>
> --
> Daniel Nordlund
> Bothell, WA  USA
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>
	[[alternative HTML version deleted]]

Clint Bowman

2015-Oct-30 19:30 UTC

head link

[R] how to work with time of day (independent of date)

Bill,

Your final words, "changes in spring and fall" reminds me of a problem
I have yet to solve.  Most of my data is logged in standard time (no 
daylight times) but often I see the note "daylight time encountered 
switching to UTC" even when I've specified "tz="PST".

I hope I've been missing something simple--any suggestions?

TIA

Clint

Clint Bowman			INTERNET:	clint at ecy.wa.gov
Air Quality Modeler		INTERNET:	clint at math.utah.edu
Department of Ecology		VOICE:		(360) 407-6815
PO Box 47600			FAX:		(360) 407-7534
Olympia, WA 98504-7600

         USPS:           PO Box 47600, Olympia, WA 98504-7600
         Parcels:        300 Desmond Drive, Lacey, WA 98503-1274

On Fri, 30 Oct 2015, William Dunlap wrote:
> You can use difftime objects to get the amount of time since the start of
> the current day.  E.g.,
>  > dateTime <- as.POSIXlt( c("2015-10-29 00:50:00",
>  + "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
>  + "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
>  + "2015-10-31 10:30:00"))
>  > date <- trunc(dateTime, units="days")
>  > sinceMidnight <- difftime(dateTime, date, units="mins")
>  > sinceMidnight
>  Time differences in mins
>  [1]   50  570 1270   50  570 1270   50  630
>
> I use difftime(x, y, units=) instead of the similar x-y because the latter
> chooses
> the units based on how far apart x and y are, while the former gives me
> consistent
> units:
>  > dateTime[1] - date[1]
>  Time difference of 50 mins
>  > as.numeric(.Last.value)
>  [1] 50
>  > dateTime[5:6] - date[5:6]
>  Time differences in hours
>  [1]  9.50000 21.16667
>  > as.numeric(.Last.value)
>  [1]  9.50000 21.16667
>
> Depending on what you are using this for, you might want to compute time
> since 3am
> of the current day so you don't get discontinuities for most times when
the
> time
> changes in spring and fall.
>
>
>
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
> On Fri, Oct 30, 2015 at 10:35 AM, Daniel Nordlund <djnordlund at
frontier.com>
> wrote:
>
>> I have a data frame with date/times represented as charaacter strings
and
>> and a value at that date/time.  I want to get the mean value for each
time
>> of day, across days, and then plot time of day on the x-axis and means
on
>> the y-axis.  R doesn't appear to have a built-in time of day time
type
>> (independent of a date), unless I have missed something. What is the
best
>> way to create a time variable so that I can aggregate and plot by time
of
>> day, with time labelled in HH:MM format.  My current approach is to
convert
>> all date/times to the same date.  I can then manage the rest of what I
want
>> with ggplot2.  But I am  wondering if there is an easier/better way to
do
>> deal with time of day.
>>
>> Here is a sample data frame.
>>
>> df <- structure(list(date = structure(1:8, .Label =
c("2015-10-29
>> 00:50:00",
>> "2015-10-29 09:30:00", "2015-10-29 21:10:00",
"2015-10-30 00:50:00",
>> "2015-10-30 09:30:00", "2015-10-30 21:10:00",
"2015-10-31 00:50:00",
>> "2015-10-31 10:30:00"), class = "factor"), value =
c(88L, 17L,
>> 80L, 28L, 23L, 39L, 82L, 79L)), .Names = c("date",
"value"), row.names >> c(NA,
>> -8L), class = "data.frame")
>>
>>
>> Any suggestions appreciated.
>>
>> Dan
>>
>> --
>> Daniel Nordlund
>> Bothell, WA  USA
>>
>> ______________________________________________
>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> 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.
>>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.
>

R help - Oct 2015 - how to work with time of day (independent of date)

[R] how to work with time of day (independent of date)

[R] how to work with time of day (independent of date)

[R] how to work with time of day (independent of date)

[R] how to work with time of day (independent of date)