dplyr :: mutate()是否不回收向量? [英] Does dplyr::mutate() not recycle vectors?

问题描述

似乎使用 dplyr :: mutate()创建列不允许向量回收.为什么?

It seems as if creating a column with dplyr::mutate() does not allow vector recycling. Why?

示例:

require(dplyr)
df <- data_frame(id = rep(1:5, each = 42), name = rep(letters[1:7], each = 6, times = 5))

现在:

df %>% mutate (tp = c(1:42))  #results in 

Error in mutate_impl(.data, dots) : 
  Column `tp` must be length 210 (the number of rows) or one, not 42

当然可以

df$tp <- c(1:42) #works

我的mutate代码是否错误，或者回收在 mutate()中根本不起作用?如果有帮助，我正在将 dplyr 0.7.2与RStudio 1.0.153(Mac)

Is my mutate code wrong or does recycling simply not work in mutate()? If it helps, I am using dplyr 0.7.2 with RStudio 1.0.153 (Mac)

推荐答案

您问了两个不同的问题:

You asked two different questions:

• (标题)"dplyr :: mutate()不回收载体吗?"

A:否(如您所知). dplyr小插图清楚地表明，回收仅适用于长度为1的向量:

A: no (as you found out). The dplyr vignette makes it clear that recycling only works for length-1 vectors:

它们[在 mutate()中使用的矢量值"必须为长度1(然后将其回收)或具有与行数相同的长度.

They [vector values used in mutate()] must be either length 1 (they then get recycled) or have the same length as the number of rows.

• 为什么?

A:如果不问 dplyr 开发人员，可能无法回答.我推测他们在便利性(一方面)与要求R的原始开发人员(甚至允许 incomplete >回收，尽管有警告).

A: Probably impossible to answer without asking the dplyr developers. I would speculate that they reached a different conclusion about the tradeoff between convenience (on the one hand) and requiring explicit statements of user intentions (on the other hand) from the original developers of R (who even allowed incomplete recycling, albeit with a warning).

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