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Select required midfieldr variables

Source: R/select_required.R
select_required.Rd

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 required by other midfieldr functions or that are required to form a composite key. 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.

...

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

select_add

Character vector of additional column names to return.

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 the default set plus any in select_add are retained; grouping structures are not preserved.

Details

Several midfieldr functions require one or more of the variables mcid, institution, race, sex, ^term, cip6, and level. And if one requires a composite key to uniquely identify rows in the course or degree tables, the variables abbrev, number and degree variable degree are also required. A vector of these names comprises the default subset.

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.

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)
#> [1] "mcid"        "institution" "race"        "sex"        
grepl(search_pattern, names(x))
#> [1] TRUE TRUE TRUE TRUE

x <- select_required(toy_term) 
names(x)
#> [1] "mcid"        "institution" "term"        "cip6"        "level"      
grepl(search_pattern, names(x))
#> [1] TRUE TRUE TRUE TRUE TRUE

x <- select_required(toy_degree) 
names(x)
#> [1] "mcid"        "institution" "term_degree" "cip6"       
grepl(search_pattern, names(x))
#> [1] TRUE TRUE TRUE TRUE

x <- select_required(toy_course) 
names(x)
#> [1] "mcid"        "institution" "term"        "abbrev"      "number"     
grepl(search_pattern, names(x))
#> [1]  TRUE  TRUE  TRUE FALSE FALSE

# Adding search terms
x <- select_required(toy_course, select_add = c("abbrev", "number", "grade")) 
names(x)
#> [1] "mcid"        "institution" "term"        "abbrev"      "number"     
#> [6] "grade"