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我有以下数据框，包括餐厅 (id#)、所有者和购买日期。有时餐厅会更改所有权，但出于分析目的，我想创建另一个仅保留最新所有者姓名的列，这由“购买日期”确定。如何创建这个新列？在此示例中，餐厅 23 于 2013 年 1 月 1 日易手，因此我只想包含新所有者的姓名 (Bob) 作为该餐厅所有行的当前所有者，如下所示。如果餐厅没有易手，请保持“当前所有者”列与“所有者”列的名称相同。

    Restaurant <- c(23,23,23,23,23,23,23,15,15,15,15,17,17,17,17)

    owner <- c("Chuck","Chuck","Chuck","Chuck","Bob","Bob","Bob",
    "Hazel","Hazel","Hazel","Hazel","Pete","Pete","Pete","Pete")

    purchaseDate <- c("3/4/2011","3/4/2011","3/4/2011","3/4/2011",
    "1/1/2013","1/1/2013","1/1/2013","4/11/2010","4/11/2010","4/11/2010",
    "4/11/2010","9/2/2012","9/2/2012","9/2/2012","9/2/2012")

    df <- data.frame( Restaurant = Restaurant, owner=owner, purchaseDate=purchaseDate)

    df$currentOwner <- c("Bob","Bob","Bob","Bob","Bob","Bob","Bob","Hazel","Hazel","Hazel","Hazel","Pete","Pete","Pete","Pete")
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1 回答 1

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你可以使用这个：

do.call(rbind, by(df, df$Restaurant, function(d)
        within(d, currentOwner2 <- as.character(
            owner[which.max(as.Date(purchaseDate, format="%d/%m/%Y"))]))))

感谢@Thomas 挖掘这个问题:-)

于 2013-07-03T21:19:08.360 回答