[R] Read in data table, change columns from factors [RESOLVED]

[David Winsemius]

> On Jul 19, 2018, at 1:21 PM, Rich Shepard <rshepard using appl-ecosys.com> wrote:
> 
> On Thu, 19 Jul 2018, David Winsemius wrote:
> 
>> I took the code that I offered earlier and replaced allyears with wy2018:
> 
>>       date  time    elev     myDate              myTime
>> 1 2017-10-01 00:00 290.298 2017-10-01 2017-10-01 00:00:00
>> 2 2017-10-01 00:30 290.301 2017-10-01 2017-10-01 00:30:00
>> 3 2017-10-01 01:00 290.304 2017-10-01 2017-10-01 01:00:00
>> 4 2017-10-01 01:30 290.295 2017-10-01 2017-10-01 01:30:00
>> 5 2017-10-01 02:00 290.292 2017-10-01 2017-10-01 02:00:00
>> 6 2017-10-01 02:30 290.289 2017-10-01 2017-10-01 02:30:00
>> 7 2017-10-01 03:00 290.289 2017-10-01 2017-10-01 03:00:00
>> 8 2017-10-01 03:30 290.289 2017-10-01 2017-10-01 03:30:00
>> 9 2017-10-01 04:00 290.280 2017-10-01 2017-10-01 04:00:00
>> 
>>> str(wy2018)
>> 'data.frame':	9 obs. of  5 variables:
>> $ date  : Factor w/ 1 level "2017-10-01": 1 1 1 1 1 1 1 1 1
>> $ time  : Factor w/ 9 levels "00:00","00:30",..: 1 2 3 4 5 6 7 8 9
>> $ elev  : num  290 290 290 290 290 ...
>> $ myDate: Date, format: "2017-10-01" "2017-10-01" ...
>> $ myTime: POSIXct, format: "2017-10-01 00:00:00" "2017-10-01 00:30:00" ...
> 
> David,
> 
>  Thank you. I see the results in the dataframe structure although I still
> don't understand all the reasons. The 'myTime' column confirms what I
> thought: that there is no separate time data type. I'll use what you taught
> me an move on with the analyses.

You can use format to only display the time portion of a datetime object. 

format( Sys.time(), "%H:%M")
[1] "13:57"

You can append the current date to a "time-only" character value and as.POSIXct will do that for you:

as.POSIXct("00:00", format="%H:%M")
[1] "2018-07-19 PDT"

> as.POSIXct(c("00:00", "00:01"), format="%H:%M")
[1] "2018-07-19 00:00:00 PDT" "2018-07-19 00:01:00 PDT"

There is a difftime-class in base R


And the lubridate package defines a duration class. It's not a package I use, and I cannot tell off the top of my head what it thinks the difference might be between a "time-span" and a "duration".

Best of luck.

> 
> Best regards,
> 
> Rich
> 
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David Winsemius
Alameda, CA, USA

'Any technology distinguishable from magic is insufficiently advanced.'   -Gehm's Corollary to Clarke's Third Law