Recode IRW Identifier Columns to Simple Sequential Codes

Replaces the values of identifier columns (by default id and item) with short ASCII codes such as P0001 and I0001. This is useful when identifiers are in a script or use characters that are awkward to type on a US keyboard, which makes subsetting, writing model formulas, and reading wide-format column names difficult.

Usage

irw_recode(df, cols = c("id", "item"), prefix = NULL)

Arguments

df: A data frame in IRW long format.
cols: Character vector of columns to recode. Defaults to c("id", "item").
prefix: Optional named character vector overriding the default code prefixes, e.g. c(item = "Q"). Defaults are "P" for id, "I" for item, and the uppercased first letter of the column name otherwise.

Value

df with the requested columns replaced by character codes and an "irw_recode_key" attribute holding a data frame with columns column, original, and code.

Details

Codes are assigned in sorted order of the unique non-missing values of each column, so they are deterministic for a given set of values. They are, however, only meaningful relative to their key: two different subsets of the same table will generally not produce the same codes.

The mapping is attached to the result as an attribute and can be retrieved with irw_recode_key(). Save it if you need it later, because most base R operations on a data frame drop attributes. The original values can be restored with irw_decode().

Note that recoding item breaks manual joins against irw_itemtext() output, which is keyed on the original item identifiers. Use irw_recode_key() to map back before joining.

Examples

df <- data.frame(
  id = c("María-01", "María-01", "René-02"),
  item = c("Q_alpha", "Q_beta", "Q_alpha"),
  resp = c(1, 0, 1),
  stringsAsFactors = FALSE
)
d <- irw_recode(df)
#> Recoded 'id': 2 unique values -> P0001..P0002
#> Recoded 'item': 2 unique values -> I0001..I0002
#> Save the mapping with irw_recode_key() if you need it later; most operations on a data frame drop attributes.
head(d)
#>      id  item resp
#> 1 P0001 I0001    1
#> 2 P0001 I0002    0
#> 3 P0002 I0001    1
irw_recode_key(d)
#>   column original  code
#> 1     id María-01 P0001
#> 2     id  René-02 P0002
#> 3   item  Q_alpha I0001
#> 4   item   Q_beta I0002
identical(irw_decode(d)$item, df$item)
#> [1] TRUE