select_required {midfieldr}

Select required midfieldr variables

Description

Subset a data frame, selecting columns by matching or partially matching a vector of character strings. A convenience function to reduce the dimensions of a MIDFIELD data table at the start of a session by selecting only those columns typically required by other midfieldr functions. Particularly useful in interactive sessions when viewing the data tables at various stages of an analysis.

Usage

select_required(midfield_x, ..., select_add = NULL)

Arguments

midfield_x

Data frame from which columns are selected, typically student, term, degree or their subsets.

...

Not used for passing values; forces subsequent arguments to be referable only by name.

select_add

Character vector of column names to be added (optionally) to the default c("mcid", "institution", "race", "sex", "^term", "cip6", "level").

Details

Several midfieldr functions are designed to operate on one or more of the MIDFIELD data tables, usually student, term, or degree. This family of functions requires only a small subset of available variables: the required columns built in to the function are mcid, institution, race, sex, ⁠^term⁠, cip6, and level. Additional column names or partial names can be included by using the select_add argument.

The column names of midfield_x are searched for matches or partial matches using grep(), thus search terms can include regular expressions. Variables with names that match or partially match the search terms are returned; all other columns are dropped. Rows are unaffected. Search terms not present are silently ignored.

One could use this function to select columns from a non-MIDFIELD data frame, but with no benefit to the user—conventional column selection syntax is better suited to that task. Here, we specialize the column selection to serve midfieldr functions.

Value

A data frame in data.table format with the following properties: rows are preserved; columns with names that match or partially match values in select_add are retained; grouping structures are not preserved.

Examples

# Default character vector for selecting columns
default_cols<- c("mcid", "institution", "race", "sex", "^term", "cip6", "level")

# Create one string separated by OR
search_pattern <- paste(default_cols, collapse = "|")

# Find names of columns matching or partially matching 
x <- select_required(toy_student) 
names(x)
grepl(search_pattern, names(x))

x <- select_required(toy_term) 
names(x)
grepl(search_pattern, names(x))

x <- select_required(toy_degree) 
names(x)
grepl(search_pattern, names(x))

x <- select_required(toy_course) 
names(x)
grepl(search_pattern, names(x))

# Adding search terms
x <- select_required(toy_course, select_add = c("abbrev", "number", "grade")) 
names(x)