[R] Date read correctly from CSV, then reformatted incorrectly by R

[Philip Monk]

Thanks, Andrew.  I didn't realise as.Date *only* read two formats, I
think I was tripped up by using %y instead of %Y, though I also know
that '/' is a special character in R (if that's the right term) and as
such know there is special syntax to use (which I don't know).

On Sat, 20 Nov 2021 at 18:02, Andrew Simmons <akwsimmo using gmail.com> wrote:
>
> The as.Date function for a character class argument will try reading in two formats (%Y-%m-%d and %Y/%m/%d).
>
>
> This does not look like the format you have provided, which is why it doesn't work. Try something like:
>
>
> x <- c("28/10/2016", "19/11/2016", "31/12/2016", "16/01/2016", "05/03/2017")
> as.Date(x, format = "%d/%m/%Y")
>
>
> which produces this output:
>
>
> > x <- c("28/10/2016", "19/11/2016", "31/12/2016", "16/01/2016", "05/03/2017")
> > as.Date(x, format = "%d/%m/%Y")
> [1] "2016-10-28" "2016-11-19" "2016-12-31" "2016-01-16" "2017-03-05"
> >
>
>
> much better than before! I hope this helps
>
> On Sat, Nov 20, 2021 at 12:49 PM Philip Monk <prmonk using gmail.com> wrote:
>>
>> Thanks Eric & Jeff.
>>
>> I'll certainly read up on lubridate, and the posting guide (again)
>> (this should be in plain text).
>>
>> CSV extract below...
>>
>> Philip
>>
>> Buffer    28/10/2016    19/11/2016    31/12/2016    16/01/2017    05/03/2017
>> 100    2.437110889    -8.69674895    3.239299816    2.443183304    2.346743827
>> 200    2.524329899    -7.688862068    3.386811734    2.680347706    2.253885237
>> 300    2.100784256    -8.059855835    3.143786507    2.615152896    2.015645973
>> 400    1.985608385    -10.6707206    2.894572791    2.591925038    2.057913137
>> 500    1.824982163    -9.122519736    2.560350727    2.372226799    1.995863839
>>
>>
>> On Sat, 20 Nov 2021 at 17:08, Philip Monk <prmonk using gmail.com> wrote:
>> >
>> > Hello,
>> >
>> > Simple but infuriating problem.
>> >
>> > Reading in CSV of data using :
>> >
>> > ```
>> > # CSV file has column headers with date of scene capture in format dd/mm/yyyy
>> > # check.names = FALSE averts R incorrectly processing dates due to '/'
>> > data <- read.csv("C:/R_data/Bungala (b2000) julian.csv", check.names = FALSE)
>> >
>> > # Converts data table from wide (many columns) to long (many rows) and creates the new object 'data_long'
>> > # Column 1 is the 'Buffer' number (100-2000), Columns 2-25 contain monthly data covering 2 years (the header row being the date, and rows 2-21 being a value for each buffer).
>> > # Column headers for columns 2:25 are mutated into a column called 'Date', values for each buffer and each date into the column 'LST'
>> > data_long <- data %>% pivot_longer(cols = 2:25, names_to = "Date", values_to = "LST")
>> >
>> > # Instructs R to treat the 'Date' column data as a date
>> > data_long$Date <- as.Date(data_long$Date)
>> > ```
>> >
>> > Using str(data), I can see that R has correctly read the dates in the format %d/%m/%y (e.g. 15/12/2015) though has the data type as chr.
>> >
>> > Once changing the type to 'Date', however, the date is reconfigured.  For instance, 15/01/2010 (15 January 2010), becomes 0015-01-20.
>> >
>> > I've tried ```data_long$Date <- as.Date(data_long$Date, format = "%d/%m.%y")```, and also ```tryformat c("%d/%m%y")```, but either the error persists or I get ```NA```.
>> >
>> > How do I make R change Date from 'chr' to 'date' without it going wrong?
>> >
>> > Suggestions/hints/solutions would be most welcome.  :)
>> >
>> > Thanks for your time,
>> >
>> > Philip
>> >
>> > Part-time PhD Student (Environmental Science)
>> > Lancaster University, UK.
>> >
>> > ~~~~~
>> >
>> > I asked a question a few weeks ago and put together the answer I needed from the responses but didn't know how to say thanks on this list.  So, thanks Andrew Simmons, Bert Gunter, Jeff Newmiller and Daniel Nordlund!
>>
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