(1)base
read.table()
read.csv()
read.delim()
write.table()
write.csv()
(2)readr
read_table()
read_csv()
read_tsv()
write_table()
write_csv()
(3)data.table
fread()
(4)rio
import()
export()
read.table()
read.csv()
read.delim()
write.table()
write.csv()
read_table()
read_csv()
read_tsv()
write_table()
write_csv()
fread()
import()
export()