为什么mutate（row_number（））对于data.tables失败？ [英] Why does mutate(row_number()) fail for data.tables?

问题描述

当我尝试在数据表上使用 dplyr 中的 row_number（）时，将引发错误。例如：

When I try to use row_number() from dplyr on a data.table, it throws an error. Here's an example:

library(dplyr)
library(data.table)
mine <- data.table(a = 1:10)
mine %>% mutate(row_number())
# Error in rank(x, ties.method = "first", na.last = "keep") : 
#   argument "x" is missing, with no default

任何想法为何

推荐答案

dplyr :: row_number（）函数有一个强制性参数，它应该是您要为其做行号的列的名称。

The dplyr::row_number() function has a mandatory parameter, which should be the name of the column that you want to do a row number for.

在您的示例中，您应该这样写：

In your example, you should have written it like this:

library(dplyr)
library(data.table)
mine <- data.table(a = 1:10) %>% 
    mutate(row_number(a))

因为 a 是您要为其添加 row_number（）的列的名称。没有这个，R就会抛出错误参数 x丢失，并且没有默认值。

Because a is the name of the column that you want to add the row_number() for. Without this, then R throws the error argument "x" is missing, with no default.

但是，我建议使用 tibble :: rowid_to_column（）函数。

However, I'd suggest using the tibble::rowid_to_column() function. It's cleaner.

library(dplyr)
library(data.table)
library(tibble)
mine <- data.table(a = 1:10) %>% 
    rowid_to_column()

我希望能帮上忙。

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