How can I append a header to a CSV file I am writing out in R?

Question

I am able to export a dataframe into CSV file but I need to append two lines of information before I do that. I don't write out the column names.

Trend data
110

Here, "Trend data" is just a text. And, 110 is the number of rows in the data frame I am writing out.

How can I append this information in the header of the csv file I am writing out in R?

Thanks!

Do you want to append it to the column names, or make a new 2 lines before the data? — Rich Scriven, Apr 05 '14 at 03:00
I don't need the column names in the file I am writing out. I want to add two new lines before the data. Thanks — Geekuna Matata, Apr 05 '14 at 03:05

score 2 · Accepted Answer · answered Apr 05 '14 at 03:17

2

This ought to do it:

x <- 1:110

writeLines(c("Trend data","110"), "myfile.dat")
write.table(x, "myfile.dat", col.names=FALSE, row.names=FALSE, append=TRUE)

Looking at it from the Mac OS X terminal:

$ head myfile.dat
Trend data
110
1
2
3
4
5
6
7
8

answered Apr 05 '14 at 03:17

hrbrmstr

77,368
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Ahh, `writeLines`... that's what I needed. After further review, mine won't work. Very nice. – Rich Scriven Apr 05 '14 at 03:19
The poster's question actually made me remember the `append` argument :-) I keep forgetting many of the `write…` functions have that. There are times that comes in really handy. – hrbrmstr Apr 05 '14 at 03:21
Right. I tried `rev(append(...` with no luck. Is there a way to reverse `append`? It prints the same result no matter which order you have the arguments listed. – Rich Scriven Apr 05 '14 at 03:21
I don't think so ([ref](http://stackoverflow.com/questions/16128001/is-it-possible-to-append-to-the-first-line-of-an-exisiting-file)). At least I've not been able to find `base` or `stats` function that wraps the process. – hrbrmstr Apr 05 '14 at 03:34
I got something with `sink`. See answer. – Rich Scriven Apr 05 '14 at 03:45

Rich Scriven · Answer 2 · 2014-04-05T03:48:04.767

You can also use write.table and sink. The sink function diverts R output to a specified file, appending it to what's already in the file, if desired.

> x <- data.frame(x = letters[1:5])

> write.table("Trend Data\n110", row.names = FALSE, 
              col.names = FALSE, quote = FALSE, file = "my.csv")
> sink("my.csv", append = TRUE)
> x
> sink()

> write.table(readLines("my.csv"), row.names = FALSE,
              col.names = FALSE, quote = FALSE)
Trend Data
110
  x
1 a
2 b
3 c
4 d
5 e

How can I append a header to a CSV file I am writing out in R?

2 Answers2