Prevent row names to be written to file when using write.csv

Question

Commands:

t <- data.frame(v = 5:1, v2 = 9:5)
write.csv(t, "t.csv")

Resulting file:

# "","v","v2"
# "1",5,9
# "2",4,8
# "3",3,7
# "4",2,6
# "5",1,5

How do I prevent first column with row index from being written to the file?

Answer 1

write.csv(t, "t.csv", row.names=FALSE)

From ?write.csv:

row.names: either a logical value indicating whether the row names of
 ‘x’ are to be written along with ‘x’, or a character vector
 of row names to be written.

• watbywbarif: I am ashamed because I did try ?write.csv but... Thx aix!
• Vanuan: Yeah, the trick is to understand that this column represents row names.
• stephanmg: Maybe one should rename this.
• Adrarc: Would there be a way to make it that row.names = FALSE is the default? It is always frustrating in complex pipelines when a single script used the TRUE default and always causes a headache...

Answer 2

For completeness, write_csv() from the readr package is faster and never writes row names

# install.packages('readr', dependencies = TRUE)
library(readr)
write_csv(t, "t.csv")

If you need to write big data out, use fwrite() from the data.table package. It's much faster than both write.csv and write_csv

# install.packages('data.table')
library(data.table)
fwrite(t, "t.csv")

Below is a benchmark that Edouard published on his site

microbenchmark(write.csv(data, "baseR_file.csv", row.names = F),
 write_csv(data, "readr_file.csv"),
 fwrite(data, "datatable_file.csv"),
 times = 10, unit = "s")
## Unit: seconds
## expr min lq mean median uq max neval
## write.csv(data, "baseR_file.csv", row.names = F) 13.8066424 13.8248250 13.9118324 13.8776993 13.9269675 14.3241311 10
## write_csv(data, "readr_file.csv") 3.6742610 3.7999409 3.8572456 3.8690681 3.8991995 4.0637453 10
## fwrite(data, "datatable_file.csv") 0.3976728 0.4014872 0.4097876 0.4061506 0.4159007 0.4355469 10