PhotoGEA (version 1.4.0)

extract.exdf: Access or modify exdf elements

Description

Returns or sets the values of elements in an exdf object.

Usage

# S3 method for exdf
[(x, i, j, return_exdf = FALSE)
  # S3 method for exdf
[(x, i, j) <- value

Value

When return_exdf is FALSE, the access operator will return either a vector or a data frame, depending on the dimension of j. When

return_exdf is TRUE, the access operator will return an

exdf object.

Arguments

x

An exdf object.

i, j

Indices specifying elements to extract or replace. Indices are numeric or character vectors or empty (missing) or NULL.

return_exdf

A logical value indicating whether the return value should be an exdf object.

value

Typically an array-like R object of a similar class as x.

Details

Since an exdf object is actually a list of named elements, those elements can be accessed using the [[ or $ operators, and a list of all named elements can be obtained by calling names.

Elements of the main_data data frame of an exdf object can be accessed and set using the [ and [<- operators. When applied to an exdf object, these operators are essentially shortcuts to calling the same operators on the object's main_data data frame.

To create a new exdf object with a subset of the data contained in another exdf object, the [ operator with return_exdf = TRUE can be used.

See Also

exdf

Examples

# Create a small exdf object that includes an extra element in addition to the
# required ones (`main_data`, `units`, and `categories`).
small_exdf <- exdf(
  data.frame(A = c(3, 2, 7, 9), B = c(4, 5, 1, 8)),
  data.frame(A = 'm', B = 's'),
  data.frame(A = 'Cat1', B = 'Cat2'),
  extra_exdf_element = "This is an example of an extra exdf element"
)

# Accessing elements of `small_exdf`
names(small_exdf)     # Get the names of all elements of small_exdf
small_exdf[['units']] # View the units using the `[[` operator
small_exdf$categories # View the categories using the `$` operator

# Accessing elements of `small_exdf$main_data`
small_exdf[,1]   # Access the first column
small_exdf[1,]   # Access the first row
small_exdf[,'B'] # Access the column named 'B'
small_exdf[1,2]  # Access element 1 of column 2

# Equivalent (but longer) commands for accessing elements of `small_exdf$main_data`
small_exdf$main_data[,1]   # Access the first column
small_exdf$main_data[1,]   # Access the first row
small_exdf$main_data[,'B'] # Access the column named 'B'
small_exdf$main_data[1,2]  # Access element 1 of column 2

# Replacing elements of `small_exdf$main_data`
small_exdf[,'A'] <- seq_len(4)             # Replace column A with new values
small_exdf[small_exdf[,'A'] > 2, 'B'] <- 0 # Replace some rows of column B with new values

# Creating a new exdf object with a subset of the data from small_exdf. Here we
# specify `return_exdf = TRUE` so that the `[` operator returns an exdf object
# instead of a data frame
new_exdf <- small_exdf[small_exdf[,'A'] > 2, , TRUE]
names(new_exdf) # Check that the `extra_exdf_element` is still present
print(new_exdf) # Check that only the rows with A > 2 are included