在数据框中选择列时出错答案

【问题标题】：Error selecting columns in dataframe在数据框中选择列时出错
【发布时间】：2016-07-25 15:55:18
【问题描述】：

这可能是一个非常简单的问题，但我仍然无法弄清楚我错在哪里。

我必须关注数据框

 Data3 <- structure(list(P1 = c("DAVID SKOCH", "VIKTOR TROICKI", "PETER LUCZAK", 
                  "SIMON STADLER", "PHILIPP PETZSCHNER", "JAMIE MURRAY", "MICHAL MERTINAK", 
                  "IGOR KUNITSYN", "DANIEL MUNOZ DE LA NAVA", "ALEXANDRE SIDORENKO"), 
           P2 = c("LOVRO ZOVKO", "DMITRI SITAK", "MARTIN VASSALLO ARGUELLO", 
                  "SEBASTIEN DE CHAUNAC", "N.SRIRAM BALAJI", "JAROSLAV LEVINSKY", 
                  "STEPHEN AMRITRAJ", "WESLEY MOODIE", "ANDREY GOLUBEV", "NICOLAS TOURTE"), 
           Date = structure(c(1167618386.44068, 1167619381.13208, 1167622892.30769, 
                                 1167626322.58065, 1167627172.88136, 1167629162.26415, 1167635959.32203, 
                                 1167636184.61538, 1167638943.39623, 1167643045.16129), tzone = "UTC", class = c("POSIXct","POSIXt")), 
           Factor = c(0.82, 1.28, 1.37, 1.37, 1.28, 1.28, 1.46, 0.73, 1.82, 1.55), Weight = c(1.1, 1.1, 1.1, 1.1, 1.1, 1.1, 1.1, 1.1, 1.1, 1.1)), 
      .Names = c("P1", "P2", "Date", "Factor", "Weight"), class = c("data.table", "data.frame"), row.names = c(NA, -10L))

我正在尝试使用的子集：

Data3[,c("Weight","Date","Factor")]

不幸的是，结果如下：

[1] "Weight" "Date"   "Factor"

而不是选择具有指定列的数据框。

有什么提示吗？

【问题讨论】：

标签： r dataframe

【解决方案1】：

我们需要使用with = FALSE，因为它是data.table。

Data3[,c("Weight","Date","Factor"), with = FALSE]

【讨论】：

或使用 data.table 语言：data3[, .(Weight, Date, Factor)]？