如何在R中处理data.table列as.character？

Question

I'm trying to use data.table rather data.frame(for a faster code). Despite the syntax difference between than, I'm having problems when I need to extract a specific character column and use it as character vector. When I call:

library(data.table)
DT <- fread("file.txt")
vect <- as.character(DT[, 1, with = FALSE])
class(vect)
###[1] "character"
head(vect)

It returns:

[1] "c(\"uc003hzj.4\", \"uc021ofx.1\", \"uc021olu.1\", \"uc021ome.1\", \"uc021oov.1\", \"uc021opl.1\", \"uc021osl.1\", \"uc021ovd.1\", \"uc021ovp.1\", \"uc021pdq.1\", \"uc021pdv.1\", \"uc021pdw.1\")

Any ideas of how to avoid these "\\" in the output?

Answer 1

The as.character works on vector s and not on data.frame/data.table objects in the way the OP expected. So, if we need to get the first column as character class, subset with .SD[[1L]] and apply the as.character

DT[, as.character(.SD[[1L]])]

If there are multiple columns, we can specify the column index with .SDcols and loop over the .SD to convert to character and assign ( := ) the output back to the particular columns.

DT[, (1:2) := lapply(.SD, as.character), .SDcols= 1:2]

data

DT <- data.table(Col1 = 1:5, Col2= 6:10, Col3= LETTERS[1:5])