R 中向量的字符频率

Question

我有一个名为的电子书文本文件Frankenstein.txt，我想知道小说中每个字母使用了多少次。

我的设置：

我像这样导入了文本文件以获得字符向量 character_array

string <- readChar("Frankenstein.txt", filesize)
character_array <- unlist(strsplit(string, ""))

character_array 给我这样的东西。

 "F" "r" "a" "n" "k" "e" "n" "s" "t" "e" "i" "n" "\r", ...

我的目标：

我想获取文本文件中每次出现字符的次数。换句话说，我想计算每个unique(character_array)

 [1] "F"  "r"  "a"  "n"  "k"  "e"  "s"  "t"  "i"  "\r" "\n" "b"  "y"  "M" 
 [15] " "  "W"  "o"  "l"  "c"  "f"  "("  "G"  "d"  "w"  ")"  "S"  "h"  "C" 
 [29] "O"  "N"  "T"  "E"  "L"  "1"  "2"  "3"  "4"  "p"  "5"  "6"  "7"  "8" 
 [43] "9"  "0"  "_"  "."  "v"  ","  "g"  "P"  "u"  "D"  "—"  "Y"  "j"  "m" 
 [57] "I"  "z"  "?"  ";"  "x"  "q"  "B"  "U"  "’"  "H"  "-"  "A"  "!"  ":" 
 [71] "R"  "J"  "“"  "”"  "æ"  "V"  "K"  "["  "]"  "‘"  "ê"  "ô"  "é"  "è" 

我的尝试 当我打电话时，plot(as.factor(character_array))我得到了一个很好的图表，它在视觉上给了我我想要的东西。 但是，我需要获取每个字符的确切值。我想要类似二维数组的东西：

    [,1]   [,2] [,3] [,4] ... 
[1,] "a"    "A"  "b"  "B" ...
[2,] "1202" "50" "12" "9" ...

Answer 1

制作此类文本处理管道的一种好方法是使用magrittr::%>% 管道。这是一种方法，假设您的文本在"frank.txt"（有关每个步骤的解释，请参见底部）：

library(magrittr)

# read the text in 
frank_txt <- readLines("frank.txt")

# then send the text down this pipeline:
frank_txt %>% 
  paste(collapse="") %>% 
  strsplit(split="") %>% unlist %>% 
  `[`(!. %in% c("", " ", ".", ",")) %>% 
  table %>% 
  barplot

请注意，您可以停在table()并将结果分配给一个变量，然后您可以根据需要对其进行操作，例如通过绘制它：

char_counts <- frank_txt %>% paste(collapse="") %>% 
  strsplit(split="") %>% unlist %>% `[`(!. %in% c("", " ", ".", ",")) %>%
  table

barplot(char_counts)

您还可以将表格转换为数据框，以便以后更轻松地操作/绘图：

counts_df <- data.frame(
  char = names(char_counts), 
  count = as.numeric(char_counts), 
  stringsAsFactors=FALSE)

head(counts_df)
## char count
##   a    13
##   b     2
##   c     7
##   d     5
##   e    24
##   f     6

每一步解释：这是完整的管道链，每一步解释：

# going to send this text down a pipeline:
frank_txt %>% 
  # combine lines into a single string (makes things easier downstream)
  paste(collapse="") %>% 
  # tokenize by character (strsplit returns a list, so unlist it)
  strsplit(split="") %>% unlist %>% 
  # remove instances of characters you don't care about
  `[`(!. %in% c("", " ", ".", ",")) %>% 
  # make a frequency table of the characters
  table %>% 
  # then plot them
  barplot

请注意，这完全等同于以下可怕的（“可怕的”？！？！）代码——前向管道%>%只是将其右侧的函数应用于其左侧的值（并且.是代词，指代左侧的值） ；见介绍小插图）：

barplot(table(
  unlist(strsplit(paste(frank_txt, collapse=""), split=""))[
    !unlist(strsplit(paste(frank_txt, collapse=""), split="")) %in% 
      c(""," ",".",",")]))