Is it possible to append to the first line of an e

问题:

I've looked at several of the functions that are able to add text to an existing data file (.csv or .txt) such as write.table, write.lines, or sink.

When the append argument =TRUE, the new data is always added after the last existing line of the file. Is it possible to add data to an existing file on first line (below a header)- AKA opposite of append?

Given a data frame:

DF <- as.data.frame(matrix(seq(20),nrow=5,ncol=4))
colnames(DF) <- c("A", "B", "C", "D")
write.table(DF, "DF.csv", row.names=FALSE, sep=",")

I can append a new data frame to the last line like this

A <- 1
A <- data.frame(A)
A$B <- 1
A$C <- 1
A$D <- 1
write.table(A, "DF.csv", row.names=FALSE, sep=",", append=TRUE, col.names=FALSE)

Which is close to what I want. But I would really like to have the above line to be added to the first line of the DF.csv (right below the header) like so

A   B   C   D
1   1   1   1
1   6   11  16
2   7   12  17
3   8   13  18
4   9   14  19
5   10  15  20

To be clear, I'd not looking to add a row into a data frame within R. I am hoping to add a row to the beginning of a file outside of the R environment. Just as append can be used to add data to the end of an external .csv file, I am hoping to "append" data to the beginning of a .csv file, so that my latest data always comes up in the first row (to avoid scrolling through to the end of a long file to see the most current data).

回答1:

Write your own function:

my.write.table <- function(df, filename, sep)
{
   ## read the existing content
   temp.df <- read.table(filename, sep)

   ## append in front
   df <- rbind(df, temp.df)

   ## write back the whole data frame
   write.table(df, filename, sep)
}