Reading and Setting Up CSV files on R Programming Language

Question

I would like to clarify my understanding here on both converting a file into CSV and also reading it. Let's use a dataset from R for instance, titled longley.

To set up a data frame, I can just use the write.table command as follows, right?

d1<-longley 
write.table(d1, file="", sep="1,16", row.names=TRUE, col.names=TRUE)

Has this already become a data frame or am I missing something here?
Now let's say if I want to read this CSV file. Then would my code be something like:

read.table(<dframe1>, header=FALSE, sep="", quote="\"")

It seems like before that I have to use a function called setwd(). I'm not really sure what it does or how it helps. Can someone help me here?

Answer 1

longley and, therefore, d1 are already data frames (type class(d1) in the console). A data frame is a fundamental data structure in R. Writing a data frame to a file saves the data in the data frame. In this case, you're trying to save the data in the data frame in CSV format, which you would do like this:

write.csv(d1, "myFileName.csv")

write.csv is a wrapper for write.table that takes care of the settings needed for saving in CSV format. You could also do:

write.table(d1, "myFileName.csv", sep=",")

sep="," tells R to write the file with values separated by a comma.

Then, to read the file into an R session you can do this:

df = read.csv("myFileName.csv", header=TRUE, stringsAsFactors=FALSE)

This creates a new object called df, which is the data frame created from the data in myFileName.csv. Once again, read.csv is a wrapper for read.table that takes care of the settings for reading a CSV file.

setwd is how you change the working directory--that is, the default directory where R writes to and reads from. But you can also keep the current working directory unchanged and just give write.csv or read.csv (or any other function that writes or reads R objects) the full path to wherever you want to read from or write to. For example:

write.csv(d1, "/path/for/saving/file/myFileName.csv")