Calculate basic stats (mean and standard error)
basic_stats.RdCalculates basic stats (mean and standard error) for each applicable column in
  an exdf object split up according to the values of one or more
  identifier columns.
Details
This function first splits up exdf_obj into chunks according to the
  values of the identifier_columns. For each chunk, columns that have a
  single unique value are identified and excluded from the statistical
  calculations. For the remaining numeric columns, the mean and standard error
  are calculated.
Value
An exdf object including the mean and standard error for each
  applicable column, where each row represents one value of the
  identifier_columns. The column names are determined by appending
  '_avg' and '_stderr' to the original names.
Examples
# Read an example Licor file included in the PhotoGEA package
licor_file <- read_gasex_file(
  PhotoGEA_example_file_path('ball_berry_1.xlsx')
)
# Calculate the average assimilation and stomatal conductance values for each
# species. (Note: this is not a meaningful calculation!)
basic_stats(
  licor_file[ , c('species', 'K', 'A', 'gsw'), TRUE],
  'species'
)
#> 
#> Converting an `exdf` object to a `data.frame` before printing
#> 
#>   species [UserDefCon] (NA) K [Const] (NA)
#> 1                   soybean            0.5
#> 2                   tobacco            0.5
#>   A_avg [GasEx] (micromol m^(-2) s^(-1))
#> 1                               23.82305
#> 2                               17.95311
#>   A_stderr [GasEx] (micromol m^(-2) s^(-1)) gsw_avg [GasEx] (mol m^(-2) s^(-1))
#> 1                                  2.470260                           0.4043737
#> 2                                  3.026751                           0.2192409
#>   gsw_stderr [GasEx] (mol m^(-2) s^(-1))
#> 1                             0.04320554
#> 2                             0.02502419