将data.table链分为两行代码以提高可读性 [英] Break data.table chain into two lines of code for readability

问题描述

我正在处理Rmarkdown文档，并被告知严格限制最大列数(空白列)为100.在文档的代码块中，我使用了许多不同的包，其中包括 data.表格.

I'm working on a Rmarkdown document, and was told to strictly limit to a maximum number of columns (margin column) of 100. In the document's code chunks I used many different packages, among which is data.table.

为了遵守限制，我可以将链条(甚至是长命令)分开，例如:

In order to comply with the limit I can split chains (and even long commands) like:

p <- ggplot(foo,aes(bar,foo2))+
       geom_line()+
       stat_smooth()
bar <- sum(long_variable_name_here,
         na.rm=TRUE)
foo <- bar %>% 
         group_by(var) %>%
         summarize(var2=sum(foo2))

但是我无法拆分 data.table 链，因为它会产生错误.我该如何实现这样的目标?

but I can't split a data.table chain, as it produces an error. How can I achieve something like this?

bar <- foo[,.(long_name_here=sum(foo2)),by=var]
           [order(-long_name_here)]

最后一行当然会导致错误.谢谢！

Last line, of course, causes an error. Thanks!

推荐答案

您必须在每行的 [和] 之间给出一个返回值.如何将 data.table 代码划分为几行的示例:

You have to give a return between the [ and ] of each line. An example for how to divide your data.table code over several lines:

bar <- foo[, .(long_name_here = sum(foo2)), by = var
           ][order(-long_name_here)]

您还可以在每个逗号之前/之后给一个回报.逗号前有返回值的示例(我的偏爱):

You can also give a return before / after each comma. An example with a return before the comma (my preference):

bar <- foo[, .(long_name_here = sum(foo2))
           , by = var
           ][order(-long_name_here)
             , long_name_2 := long_name_here * 10]

有关扩展示例，请参见此答案

See this answer for an extended example

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