التجميع وإعادة التشكيل والربط

d <- data.frame(group = c("a", "b", "a"), minutes = c(2, 10, 4), stringsAsFactors = FALSE)
s <- aggregate(list(total = d$minutes), by = list(group = d$group), FUN = sum)
s <- s[order(s$group), , drop = FALSE]
cat("groups=", paste(s$group, collapse = ","), "\n", sep = "")
cat("totals=", paste(s$total, collapse = ","), "\n", sep = "")
cat("preserved total=", sum(s$total) == sum(d$minutes), "\n", sep = "")

groups=a,b
totals=6,10
preserved total=TRUE

يعطي التجميع ملخصاً لكل مجموعة، ويفيد حفظ المجموع كثابت لهذه القيم الكاملة المنتهية.

left <- data.frame(id = c("a", "b", "c"), value = c(1, 2, 3), stringsAsFactors = FALSE)
right <- data.frame(id = c("a", "a", "b"), tag = c("x", "y", "z"), stringsAsFactors = FALSE)
joined <- merge(left, right, by = "id", all.x = TRUE, sort = TRUE)
cat("left rows=", nrow(left), "; joined rows=", nrow(joined), "\n", sep = "")
cat("a rows=", sum(joined$id == "a"), "; unmatched=", sum(is.na(joined$tag)), "\n", sep = "")

left rows=3; joined rows=4
a rows=2; unmatched=1

تنتج المفاتيح اليمنى المكررة مطابقات متعددة؛ وحفظ مفاتيح اليسار لا يحفظ عدد صفوفه.