How can you merge two data frames in R?
Instruction: Provide an example to illustrate how to merge two data frames by a common column in R.
Context: This question checks the candidate's ability to manipulate and combine data sets, a common task in data analysis.
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Use merge with an explicit key. Its default is an inner join; all.x=TRUE keeps every row from the left data frame.
sales <- data.frame(product_id = c(1, 1, 2, 3), amount = c(10, 20, 30, 40)) products <- data.frame(product_id = c(1, 2), name = c("A", "B")) stopifnot(!anyDuplicated(products$product_id)) result <- merge(sales, products, by = "product_id", all.x = TRUE) result <-...