R语言merge函数报错：'by'必须指定唯一有效列求助

错误原因 #

你执行merge时犯了一个低级错误：把y参数传成了向量ProductPurchased，但merge要求x和y必须都是数据框类型。向量里根本没有名为"Emails"的列，自然会触发'by' must specify a uniquely valid column的报错。

修正后的代码 #

把y = ProductPurchased改成你之前创建的Purchases数据框即可，完整代码如下：

Emails <- c("Bob@gmail.com","Mike@aol.com","Lyndsey@blue.com","Ethan@gmail.com","Sara@gmail.com",
           "Sarah@yahoo.com","Leo@stuff.com","Raj@blue.com")
State <- c("Washington","California","Texas","Iowa","New York","California","Alabama","Alaska")
PPP <- data.frame(Emails = Emails,State = State)

Emails <- c("Bob@gmail.com","Mike@aol.com","Lyndsey@blue.com","Ethan@gmail.com","Sara@gmail.com",
           "Sarah@yahoo.com","Leo@stuff.com","Raj@blue.com","Lyndsey@blue.com","Ethan@gmail.com","Sara@gmail.com",
           "Sarah@yahoo.com","Leo@stuff.com","Raj@blue.com","Mike@aol.com","Lyndsey@blue.com","Ethan@gmail.com","Sara@gmail.com",
           "Sarah@yahoo.com","Leo@stuff.com")
ProductPurchased <- c("Hat","Bat","Cat","Hat","Candy","Fruit","Candy","Cat","Hat","Candy","Fruit",
                      "Candy","Cat","Hat","Candy","Fruit","Candy","Cat","Hat","Candy")
Purchases <- data.frame(Emails = Emails,ProductPurchased = ProductPurchased)

# 修正后的左连接语句
Left <- merge(x = PPP, y = Purchases, by.x = "Emails", by.y = "Emails", all.x = TRUE)

效果说明 #

修正后执行代码，就能正常完成左连接：PPP里的所有用户都会被保留，有购买记录的用户会对应显示购买的产品，没有购买记录的用户（比如Bob）的ProductPurchased列会显示为NA。

内容的提问来源于stack exchange，提问作者Michael Cantrall