Formula Interfaces

Aggregate Formula

Response by Group

Many base R functions accept a formula. In score ~ group, the left side is summarized separately for each right-side group.

Program

Play the script to add a selected bonus, then summarize scores by group with formula syntax.

aggregate_formula.R 
scores <- data.frame(group = c("A", "A", "B", "B"), score = c(8, 10, 6, 12))
bonus <- 
scores$score <- scores$score + bonus
summary <- aggregate(score ~ group, data = scores, FUN = mean)
label <- paste(summary$group, summary$score, collapse = "; ")
cat(label, "\n", sep = "")

scores <- data.frame(group = c("A", "A", "B", "B"), score = c(8, 10, 6, 12))
bonus <- 
scores$score <- scores$score + bonus
summary <- aggregate(score ~ group, data = scores, FUN = mean)
label <- paste(summary$group, summary$score, collapse = "; ")
cat(label, "\n", sep = "")

scores <- data.frame(group = c("A", "A", "B", "B"), score = c(8, 10, 6, 12))
bonus <- 
scores$score <- scores$score + bonus
summary <- aggregate(score ~ group, data = scores, FUN = mean)
label <- paste(summary$group, summary$score, collapse = "; ")
cat(label, "\n", sep = "")
formula `score ~ group` reads as summarize `score` by `group`.
aggregate `aggregate(formula, data, FUN)` applies a summary to each group.
data argument `data = scores` tells R where to find the formula names.