如何将半结构化TXT代码书转换为R语言Data Frame？

问题背景 #

我有一个作为大型数据集代码书的半结构化.txt文件，结构示例如下：

==============================                                                
VAR V960922                                                                    
              NUMERIC                                                         
                                                                              
         Admin.48                                                             
                                                                              
         SUMMARY - POST MODE ASSIGNMENT AND ADMINISTRATION                    
         -----------------------------------------------------------          
                                                                              
              Post mode in this variable refers to beginning mode             
              (question Admin.47).                                            
                                                                              
        749      1.   Assigned to personal, administered as                   
                      personal IW                                             
          7      2.   Assigned to personal, administered as                   
                      telephone IW                                            
         28      3.   Assigned to telephone, administered as                  
                      personal IW                                             
        750      4.   Assigned to telephone, administered as                  
                      telephone IW                                            
                                                                              
                 0.   Inap, no Post IW                                        
                                                                              
============================== 

希望将该结构转换为Data Frame用于后续数据清洗与标注，理想输出格式如下：

| Var Name | Frequencies | Value Labels
| -------- | ----------- | ---------------------------------------------------
| V960922  |        749  | 1. Assigned to personal, administered as personal IW
| V960922  |          7  | 2. Assigned to personal, administered as telephone IW
| V960922  |         28  | 3. Assigned to telephone, administered as personal IW
| V960922  |        750  | 4. Assigned to telephone, administered as telephone IW
| V960922  |         NA  | 0. Inap, no Post IW
     

文件中各变量结构类似，但值数量、摘要长度有差异。

我目前用readLines读取文件，通过str_subset提取行来拼接Data Frame：

nes <- readLines("nes1996var.txt")
 
vars <- str_subset(nes, "^VAR")
vars


numbers <- str_subset(nes,"\\d?\\.")
numbers

提取变量名成功，但提取表格时遇到困难：行首空白导致无法按行首数字筛选；用"数字+句号"筛选会误捕无关内容，且多行标签会被截断；还无法分离同一行的频率与标签。

可行解决方案 #

经调整后，以下方案可实现需求：

rl <- readLines("你的txt文件路径")

## 去除每行首尾的空白字符
## 这样频率值会成为对应行的起始内容
rl <- trimws(rl)

## 定位分隔变量的分隔符行
delims <- grep("==============================", rl)

## 初始化输出列表
out <- vector(mode="list", length=length(delims)-1)

## 遍历每个变量块
for (i in 1:(length(delims) - 1)) {
  ## 提取相邻分隔符之间的内容作为单个变量的信息
  vbl <- rl[(delims[i] + 1):(delims[(i + 1)] - 1)]
  ## 从第一行提取变量名（截取"VAR "之后的内容）
  varname <- gsub("VAR (.*)", "\\1", vbl[1])
  ## 定位以数字开头的行（对应频率和标签的起始行）
  resps <- grep("^\\d", vbl)
  
  if (length(resps) > 0) {
    ## 找到最后一个响应行之后最近的空白行，作为最后一个响应类别的结束标记
    blanks <- which(vbl == "")
    resps <- c(resps, blanks[min(which(blanks > max(resps)))])
    ## 提取频率值，移除最后一个空白行对应的无效值
    freqs <- gsub("^(\\d+).*", "\\1", vbl[resps])
    freqs <- freqs[-length(freqs)]
    ## 拼接每个响应类别的多行标签内容
    vlabs <- sapply(1:(length(resps) - 1), function(j) {
      paste(vbl[resps[j]:(resps[(j + 1)] - 1)], collapse = " ")
    })
    ## 移除标签开头的频率值和空白字符，并清理标签首尾空白
    vlabs <- trimws(gsub("^\\d+\\s+(.*)", "\\1", vlabs))
    ## 将变量名、频率、标签整合为Data Frame
    out[[i]] <- data.frame(`Var Name` = varname, Frequencies = freqs, `Value Labels` = vlabs)
  } else {
    ## 无响应行时生成空Data Frame
    out[[i]] <- data.frame(`Var Name` = character(0), Frequencies = character(0), `Value Labels` = character(0))
  }
}

## 最后将所有变量的Data Frame合并为一个大表
final_df <- do.call(rbind, out)

注意：代码中需将"你的txt文件路径"替换为实际文件路径；最后一行的合并操作可根据需求选择是否执行。

内容的提问来源于stack exchange，提问作者Thomas