How to append a whole dataframe to a CSV in R

Question

I can already append a row to a CSV using cat which makes that very easy:

  cat(\"my row, 1, 2, 3, 4\", \"mydf.csv\",sep=\"\\n\", append=TRU         


        

Answer 1

If you have enough memory, the most efficient way is to bind them all together then write to file:

df <- cbind(df1, df2, df3)
write.csv(df, "spam.csv")

Otherwise, you can use the append argument in write.csv:

dfs <- c(df1, df2, df3)
for (df in dfs){
  write.csv(df, "eggs.csv", append = TRUE)
}

Answer 2

Another workaround (using cat) is that you transpose your data frame, then append a row containing only "\n" using rbind, then converting this data frame to a vector (it will have "\n" after every 'row') which will now show up in your csv file as a data frame.

Below an example:

df <- rbind(t(df),"\n")
cat(c("",df),sep=",",append=TRUE)

Note: my assumption is that you have opened a connection to a file using sink(filepath/filename.csv).

Answer 3

Ok so I realised that append=T does work with write.table - but write.table needs the sep switch to be used so this works:

write.table(myDF, "myDF.csv", sep = ",", col.names = !file.exists("myDF.csv"), append = T)