r - Extract value from tibble in R markdown inline code

Question

I'm looking to access a value from a tibble using inline code in an R Markdown document.

The following code gives me a 1 x 2 tibble.

#library(tidyverse)
#library(knitr)

# Minimal working example
df <- tibble(
  Event = c("Swimming","Swimming","Swimming","Camping","Hiking","Hiking")
)
df

# Creates 1 row x 2 column
df %>% count(Event) %>% slice(which.max(n))

If I create an object in a code chunk, I can select [1,1] and report that inline:

temp <- df %>% count(Event) %>% slice(which.max(n))

# The most popular event was `r temp[1,1]`.

# which becomes "The most popular event was Swimming."

Is there a way to do that within my dplyr pipes without creating a new object? Ideally, I would be able to do it all via inline code, something like:

`r df %>% count(Event) %>% slice(which.max(n)) %>% df[1,1]`  # fails

Stepping back, I'm looking for a generalizable technique to use to select particular rows and cells from within a series of dplyr commands without creating new objects along the way.

标签： rdplyrr-markdownknitrtibble

Answer 1

即使不在 R Markdown 中，您想要显示内联的代码行也不会运行，请在控制台中尝试。在管道中使用特殊运算符（如[, [[, ）$时，您需要以前缀而不是像其他函数那样的中缀形式指定它们，像这样。请注意您尝试的代码的比较，或者使用[[向下钻取并仅选择文本而不是返回小标题。

library(tidyverse)
df <- tibble(
  Event = c("Swimming","Swimming","Swimming","Camping","Hiking","Hiking")
)

df %>% count(Event) %>% slice(which.max(n)) %>% `[`(1,1)
#> # A tibble: 1 x 1
#>   Event   
#>   <chr>   
#> 1 Swimming
df %>% count(Event) %>% slice(which.max(n)) %>% `[[`("Event")
#> [1] "Swimming"

但是，这并不能完全解决您的问题，因为 R Markdown 使用反引号来表示内联代码，并且更改knitr用于查找和评估内联代码的解析规则很复杂，因此这里它会认为代码以`[`. 因此，您可以改为使用magrittr这些函数的别名，extract并extract2在内联代码中：

Most popular event was `r df %>% count(Event) %>% slice(which.max(n)) %>% magrittr::extract2("Event")`

Most popular event was Swimming在渲染的降价中正确打印。