读取、子集“选择”并在R中写入TXT文件

假设文件在末尾的注释中重复创建:

library(sqldf)

read.csv.sql("File1.txt", 
  "select V2, V3, V4 from file where V1 = 'abc'", header = FALSE, sep = " ")

给:

  V2 V3 V4
1  1  6  a
2  2  7  b
3  4  9  d

注释

Lines <- "abc 1 6 a
abc 2 7 b
efg 3 8 c
abc 4 9 d
efg 5 10 e
"
cat(Lines, file = "File1.txt")

下面有助于回答来自csvfile的子集数据吗?

library(sqldf);
read.csv.sql(file, sql = "select * from file", header = TRUE, sep = ",")

说明 用SQL语句将文件读取到r中并对其进行筛选。只有过滤部分由R处理,所以 可以容纳大于r所能处理的文件。

这应该是所有需要的,记住 like() 来自 data.table 程序包使用 grepl 在内部,所以我认为regex可能也是一个选项。

library(data.table)
# Depending on the characteristics of the csv file this call has to be adjusted
dt <- data.table(read.csv("File1.txt", header = FALSE, sep = " "))
# or
dt <- fread("test.txt")
# data.table looks like this after import
dt <- structure(list(V1 = structure(c(1L, 1L, 2L, 1L, 2L)
      , .Label = c("abc", "efg")
      , class = "factor")
      , V2 = 1:5
      , V3 = 6:10
      , V4 = structure(1:5, .Label = c("a", "b", "c", "d", "e")
      , class = "factor")), row.names = c(NA, -5L)
      , class = c("data.table", "data.frame"))

write.csv(dt[like(V1, "abc"), .(V2
                      , V3
                      , V4
                      )],file = "File2.txt", row.names = FALSE)