[R] Dates as headers causing confusion but needed to convert to Julian days for ANOVA

[Jeff Newmiller]

You did not say which function you used to import the csv file, but it looks like you probably used read.csv without setting the check.names argument to FALSE.

Whether you change that out not, once you have reshaped the data, you can use a format specifier with as.Date to extract a date. (See ?strptime for format string specifiers.)

On October 25, 2021 7:09:24 AM PDT, Philip Monk <prmonk using gmail.com> wrote:
>Hello,
>
>First post - apologies if I get anything wrong - either in describing the
>question (I've only been using R for a week) or etiquette.
>
>I have CSV files of Land Surface Temperature (LST) data derived from
>Landsat 8 data and exported from Google Earth Engine.  I am investigating
>whether the construction of utility-scale solar power plants affects the
>local climate.
>
>I need to tidy the CSV files so that I can use Two-way ANOVA w/repeated
>measures but am having problems due to column headers (necessarily, I
>think) being dates.
>
>Each CSV currently has the following columns:
>
>Buffer
>Values 100-2000 in 100 increments.  Buffers are 100m wide and extend
>outwards from each site boundary.
>
>24 columns of monthly data.
>Column headers are in date format (currently dd/mm/yyyy in Excel) and
>relate to the date on which the original Landsat 8 image from which the LST
>data are derived was captured.
>I need these dates to calculate the 'Julian day' (1-365.25) for each month,
>and also to extract the Year.
>
>Time
>Currently 1 = pre-construction and 2 = post-construction.
>
>The data frame created when importing one of these CSV's into R looks like
>this:
>
>'data.frame':	20 obs. of  14 variables:
> $ Buffer     : int  100 200 300 400 500 600 700 800 900 1000 ...
> $ X15.01.2010: num  6.09 5.27 4.45 3.39 2.9 ...
> $ X16.02.2010: num  6.41 5.99 5.61 4.78 4.31 ...
> $ X20.03.2010: num  8.93 7.38 6.12 5.61 5.61 ...
> $ X24.04.2011: num  6.28 5.81 5.15 4.54 4.32 ...
> $ X07.05.2010: num  6.13 5.54 5.35 4.82 4.52 ...
> $ X08.06.2010: num  7.71 7.4 6.82 6.14 5.82 ...
> $ X13.07.2011: num  4.07 2.93 2.69 2.47 2.53 ...
> $ X11.08.2010: num  5.96 5.68 5.38 4.96 4.57 ...
> $ X12.09.2010: num  5.76 5.15 4.54 3.87 3.46 ...
> $ X17.10.2011: num  3.16 2.51 2.51 2.06 2.01 ...
> $ X15.11.2010: num  4.72 3.77 3.24 2.74 2.49 ...
> $ X01.12.2010: num  4.26 3.516 2.154 1.056 0.315 ...
> $ Time       : int  1 1 1 1 1 1 1 1 1 1 ...
>
>
>Importing a CSV into R that has a date as a column header (in whatever
>format) causes problems!  R adds the 'X', and converts the separator.
>
>I was using 'gather' and 'pivot_longer' (see below) but the date issue has
>wrecked that approach.  I've tried reformating the date, trying to remove
>the X, and going away to learn more about data frames, dplyr, and readr.
>I'm not making any progress, though, and I'm just getting more confused.
>
>Helped requested
>~~~~~~~~~~~~~~
>
>How should I proceed to tidy the data such that I can:
>
>*) extract the year and Julian day for each date, then convert the date to
>the name of the month?
>*) create a tidy table with columns for Buffer, Month, Year, Julian day,
>LST (the values), and Time (1 = pre-construction, 2 = post-construction of
>a solar farm).
>
>Prior to deciding I needed to calculate the Julian day for use in ANOVA I
>was doing this (with month names rather than dates - please remember I'm a
>newbie!):
>
>data <- read.csv(...
>attach(data)
># data_long <- data %>% pivot_longer(!Buffer, names_to = "month", values_to
>= "LST")
># data_long <- data %>% pivot_longer(!Buffer, names_to = c("month",
>"Time"), names_sep = 13, values_to = "LST")
>data_long <- gather(data, Month, LST, January:December, factor_key=TRUE)
>data_long$Time <- as.factor(data$Time)
>str(data_long)
>
>'pivot_longer' didn't work, but 'gather' did to create the long data needed
>for ANOVA.
>
>For example:
>
>'data.frame': 480 obs. of  4 variables:
> $ Buffer: int  100 200 300 400 500 600 700 800 900 1000 ...
> $ Time  : Factor w/ 2 levels "1","2": 1 1 1 1 1 1 1 1 1 1 ...
> $ Month : Factor w/ 12 levels "January","February",..: 1 1 1 1 1 1 1 1 1 1
>...
> $ LST   : num  NA 0.803 0.803 1.044 0.475 ...
>
>Suggestions/hints/solutions would be most welcome.  :)
>
>Thanks for your time,
>
>Philip
>
>Part-time PhD Student (Environmental Science)
>Lancaster University, UK.
>
>	[[alternative HTML version deleted]]
>
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-- 
Sent from my phone. Please excuse my brevity.