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

[Philip Monk]

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!