将 magrittr 与 (*)apply 函数一起使用 - 不同的输出

Question

我将文件读入包含一列字符的 data.frame，并使用 sapply 按元素应用一些函数。我对使用 magrittr 包中的 pipes 很感兴趣，我想知道这样做的正确和最佳方法是什么。我已经尝试了一些变体，虽然它有效（我相信！），但两种方法的输出确实不同。

我省略了 sapply 本身的占位符，作为下一个函数的 %>% pipes into the first parameter。

原始代码

## Load in a CSV file as a dataframe
   y <- read.csv(file = file_name, header = TRUE, sep = "\n", quote = "", row.names = NULL, stringsAsFactors = FALSE)
## Perform so operations
y$transformed1 <- sapply(y, FUN = function(x) gsub("&amp;", "&", x))
y$transformed2 <- sapply(y$transformed1, FUN = function(x) gsub(pattern = "http\\S+\\s*", replacement = "", x)) 
y$transformed3 <- sapply(y$transformed2, FUN = function(x) gsub("[^[:alpha:][:space:]&\']", "", x)) 
y$transformed4 <- sapply(y$transformed3, FUN = function(x) stripWhitespace(x)) 
y$transformed5 <- sapply(y$transformed4, FUN = function(x) gsub("^ ", "", x))
y$transformed6 <- sapply(y$transformed5, FUN = function(x) gsub(" $", "", x))

这对我来说非常有用，在y$transformed6 中返回满足我需要的干净结果。

使用magrittr

以下代码运行良好，通过目视检查，结果看起来相同，如下面的head 函数比较所示。

in_file <- y   ## from above

out_file <-  sapply(in_file, function(x) gsub("&amp;", "&", x)) %>%
                    gsub("http\\S+\\s*", "", .) %>%
                    gsub("[^[:alpha:][:space:]&\']", "", .) %>%
                    stripWhitespace() %>%
                    gsub("^ ", "", .) %>%
                    gsub(" $", "", .)

在这里，您可以看到每个输出的 str() 和 head() 函数的返回值。在它们上使用identical 函数不出所料地返回FALSE。

## First method

> str(y$transformed6)                                
 chr [1:14158] "ExchangeNews Direct S&P Dow Jones Ind

> head(y$transformed6)                               
[1] "ExchangeNews Direct S&P Dow Jones Indices Announ
[2] "Svelte Medical Systems Raises M for HeartSurgery
[3] "Dow Jones industrial average tumbles below on bu
[4] "Dow approaches record high as Fed meeting begins
[5] "Money How the Dow Jones industrial average did T
[6] "Just another day at dowjones brewing up exciting

-----------------------------------------------------

## Using magittr

> str(out_file)                                      
 chr [1:14158, 1] "ExchangeNews Direct S&P Dow Jones 
 - attr(*, "dimnames")=List of 2                     
  ..$ : NULL                                         
  ..$ : chr "text"                                   

> head(out_file)                                     
     text                                            
[1,] "ExchangeNews Direct S&P Dow Jones Indices Annou
[2,] "Svelte Medical Systems Raises M for HeartSurger
[3,] "Dow Jones industrial average tumbles below on b
[4,] "Dow approaches record high as Fed meeting begin
[5,] "Money How the Dow Jones industrial average did 
[6,] "Just another day at dowjones brewing up excitin

差异究竟来自哪里？我做错了什么还是只是使用magittr 的产物？

Answer 1

您应该将管道放在sapply 内，而不是之后

out_file <-  sapply(in_file, function(x) {gsub("&amp;", "&", x) %>%
    gsub("http\\S+\\s*", "", .) %>%
    gsub("[^[:alpha:][:space:]&\']", "", .) %>%
    stripWhitespace() %>%
    gsub("^ ", "", .) %>%
    gsub(" $", "", .)
})