R中有数据表的怪异情况，列名混合 [英] Weird case with data tables in R, column names are mixed

问题描述

因此，我在名为 mc_with_devices 的数据表中创建了一个名为 mc_split_device 的变量.但是，如果我键入 mc_with_devices $ mc_split ，则会得到列 mc_split_device 的值，而我从未创建任何名称为 mc_split 的变量.

解决方案

请参见哈德利·威克姆(Hadley Wickham)的Advanced R :

$是一个简写运算符，其中x $ y等于x [["y"，确切= FALSE]].通常用于访问数据帧中的变量，例如mtcars $ cyl或diamonds $ carat.

所以 exact = FALSE 是 $ mc_split 起作用的原因，尽管没有确切名称的列.

顺便说一句，我不相信 mc_with_devices [，..(mc_split)] 在没有双引号的情况下也可以使用.以下将起作用:

mc_with_devices [，"mc_split_resp"]

So I have created this variable that is called mc_split_device inside the datatable called mc_with_devices. However, If I type mc_with_devices$mc_split I get the values of the column mc_split_device while I never created any variable with the name mc_split.

解决方案

See Hadley Wickham's Advanced R:

$ is a shorthand operator, where x$y is equivalent to x[["y", exact = FALSE]]. It’s often used to access variables in a data frame, as in mtcars$cyl or diamonds$carat.

So the exact=FALSE is the reason why $mc_split works despite there not being a column with that exact name.

As an aside, I don't believe mc_with_devices[,.(mc_split)] will work without doublequotes. The following will work:

mc_with_devices[,"mc_split_resp"]

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