如何使用 R 读取带有两个双引号作为文本限定符的 csv？

Question

如何在 csv 中读取 2 个双引号作为限定符，并在限定符中使用逗号，即

""V"",""W"",""X"",""Y"",""Z""
""            "",""A                    "",""*B           "",""C                  "",""D-E""
""            "",""a                     "",""*b            "",""c,c,c"",""d e         ""
""            "",""E                    "",""*F           "",""G                   "",""H-H""

在data.table 中使用fread？

Answer 1

根据要求使用data.table 和fread，您可以执行此操作。

诀窍是

1. 通过设置sep='~'（或文件中不存在的其他字符）和设置quote=''（无引号）将文件中的每一行作为一个列读取。
2. 然后，删除行首和行尾的双引号
3. tstrsplit() 使用"","" 作为模式将单列分成多列

data.table::tstrsplit() 是strsplit() 的便捷包装器，可将转置为列的行返回。

R 代码：

library(data.table)
# Read the file as a single column per line by picking 
#  a sep character that doesn't exist in the file. 
#  E.g. '~' doesn't exist in the OP's current sample data

DT <- fread( "OPs_new_input_example_file.csv", 
             sep='~', quote='', header=FALSE)

DT[, V1 := gsub('""(.*)""$', "\\1",V1)] # remove "" at start and end
DT <- DT[, tstrsplit(V1, '"",""') ] # strsplit and transpose rows to columns
DT

结果：

             V1                     V2             V3                   V4           V5
1:            V                      W              X                    Y            Z
2:               A                      *B             C                            D-E
3:              a                      *b                            c,c,c d e         
4:               E                      *F            G                   

请随时发布改进建议或替代解决方案。