Generate Integer Group Indices — Getgroupindex • mwivhet

Converts a grouping variable into a vector of contiguous integer indices ranging from 1 to \(G\), where \(G\) is the number of unique groups. This is a helper function used to facilitate matrix indexing for group-level variance calculations.

Getgroupindex(ds, group)

Arguments

ds: Data frame. The dataset containing the grouping variable.
group: Name of the grouping variable (passed as an unquoted symbol) within ds. This variable defines the clusters (e.g., judges, examiners, or time periods).

Value

An integer vector of length \(n\), containing values in \(\{1, \dots, G\}\).

Details

The function extracts the specified group column from the data frame using non-standard evaluation. It then maps each unique value of the group to an integer index corresponding to its order of appearance in unique(group).

This transformation is functionally equivalent to as.numeric(as.factor(group)), but ensures explicit handling within the provided data frame context.

Examples

data <- data.frame(judge_id = c("JudgeA", "JudgeB", "JudgeA", "JudgeC"))
Getgroupindex(data, judge_id)
#> [1] 1 2 1 3