fread
{data.table}在使用标签分隔文件时出现问题,该文件具有部分引用的行。我无法找到解决方法,因为它会自动处理引号(因此quote
没有read.csv
参数。这表明:
str1 = 'L1\tsome\tunquoted\tstuff\nL2\tsome\t"half" quoted\tstuff\nL3\tthis\t"should work"\tok thought'
str2 = gsub('"', '', str1)
fread(str2, sep='\t', header=F, skip=0L)
# V1 V2 V3 V4
# 1: L1 some unquoted stuff
# 2: L2 some half quoted stuff
# 3: L3 this should work ok thought
fread(str1, sep='\t', header=F, skip=0L)
# Error in fread(str1, sep = "\t", header = F, skip = 0L) :
# Expected sep (' ') but '
# ' ends field 3 on line 1 when detecting types: L2 some "half" quoted stuff
有没有办法解决这个问题,除了在原始文件上执行查找/替换之外?
答案 0 :(得分:2)
stringi
呢?很容易理解,非常有效。还有一个函数stri_read_lines()
,用于从文件中读取/分割行。
library(stringi)
as.data.frame(stri_split_fixed(stri_split_lines1(str1), "\t", simplify = TRUE))
# V1 V2 V3 V4
# 1 L1 some unquoted stuff
# 2 L2 some "half" quoted stuff
# 3 L3 this "should work" ok thought
如果您需要确信这是一种比read.*()
更有效的方法,请在应用于解析为30k行的扁平字符串时查看上述方法的时序。您还可以通过调整as.data.frame()
中的参数来加快速度。对于此示例,stringi
方法的速度大约是read.table()
的两倍。
str1 <- "L1\tsome\tunquoted\tstuff\nL2\tsome\t\"half\" quoted\tstuff\nL3\tthis\t\"should work\"\tok thought"
library(stringi)
library(microbenchmark)
write(stri_flatten(rep(str1, 1e5), collapse = "\n"))
file.info("data")[1]
# size
# data 8400000
microbenchmark(
stringi = {
mat <- stri_split_fixed(stri_read_lines("data"), "\t", simplify = TRUE)
out <- as.data.frame(mat)
},
read.table = {
out2 <- read.table("data", sep = "\t", quote = "\n")
},
times = 3L,
unit = "relative"
)
# Unit: relative
# expr min lq mean median uq max neval cld
# stringi 1.000000 1.000000 1.000000 1.000000 1.00000 1.000000 3 a
# read.table 2.074071 2.111722 1.997857 2.148897 1.96356 1.808365 3 b
identical(out, out2)
# [1] TRUE