R Input and Output

This tutorial describes you about the various input / output features that are available and its implementation within R programming.

Reading from the Keyboard

Now you can use scan():

> z <- scan()
1: 12 5
3: 2
4:

Read 3 items

> z
[1] 12 5 2

You can use readline() for inputing a line from the keyboard in the form of a string:

> w <- readline()
xyz vw u
> w
[1] "xyz vw u"

Printing to the Screen

In interactive mode, one can print the value of that variable by just typing the variable name or expression. In batch mode, one can use the print() function, e.g.

print(x)

The argument might be an object. So it is a little better to use cat() instead of print(), as the last one can print only one expression and its result is numbered, which may be a nuisance to us. Here is an example written below:

> print("xyz")
[1] "xyz"
> cat("xyz \n")
xyz

The arguments to cat() will be printed out with intervening spaces, for instance

> g <- 62
> cat(g,"xyz","gs\n")
62 kyz gs

Reading a Matrix or Data Frame from a File

The function read.table() is used usually. Here is a somewhat more about it:
The default value of a header is 'FALSE' and hence when you do not have a header, you need not say such.

Basically, the character strings are considered as R factors. For turning this "feature" off, you can include the argument as.is=T in your call to read.table().

When you have a spreadsheet export file, i.e. having a type .csv where the fields are divided by commas in place of spaces, use read.csv() in place of read.table(). You can also use read.xls for reading core spreadsheet files.

It is to be noted that when you read in a matrix using read.table(), the resultant object will become a data frame, even when all of the entries got to be numeric. You may need it in the form of a matrix, where the case do a followup call towards as.matrix().

For example, let say the matrix x becomes:

1 0 1
1 1 1
1 1 0
1 1 0
0 0 1

You can read it into a matrix form like this

> x <- matrix(scan("x"),nrow=5,byrow=T)

Reading a single File One Line at a Time

You can use readLines() for this. You need to produce a connection first, by calling the file(). Here is a simple example below:

> c <- file("z","r")
> readLines(c,n=1)
[1] "1 3"

Writing a Table to a File

R uses the function write.table() that works very much similar to read.table()which writes a data frame instead of reading one. In the case of writing a matrix, to a file, you just need not have to know row or column names like:

> write.table(xc,"xcnew",row.names=F,col.names=F)