read.table Function in R (2016): A Comprehensive Guide

The post is about how to import data using read.table() function in R. You will also learn what is a file path and how to get and set the working directory in R language. The read.table() function in R is a powerful tool for importing tabular data, typically from text files, into the R environment. The read.table function converts the tabular data from a flat-file format into a more usable data structure called the data frame.

Question: How can I check my Working Directory so that I would be able to import my data in R? Answer: To find the working directory, the command getwd() can be used, that is

getwd()
import data using read.table function in R

Question: How can I change the working directory to my path?
Answer: Use function setwd(), that is

setwd("d:/mydata")
setwd("C:/Users/XYZ/Documents")

Import Data using read.table Function in R

Question: I have a data set stored in text format (ASCII) that contains rectangular data. How can I read this data in tabular form? I have already set my working directory.
Answer: As data is already in a directory set as the working directory, use the following command to import the data using read.table() command.

mydata <- read.table("data.dat")
mydata <- read.table("data.txt")

The mydata is a named object that will have data from the file “data.dat” or “data.txt” in data frame format. Each variable in the data file will be named by default V1, V2,…

Question: How this stored data can be accessed?
Answer: To access the stored data, write the data frame object name (“mydata”) with the $ sign and name of the variable. That is,

mydata$V1
mydata$V2
mydata["V1"]
mydata[ , 1]

Question: My data file has variable names in the first row of the data file. In the previous question, the variable names were V1, V2, V3, … How can I get the actual names of the variables stored in the first row of the data.dat file?
Answer: Instead of reading a data file with default values of arguments, use

read.table("data.dat", header = TRUE)

Question: I want to read a data file that is not stored in the working directory.
Answer: To access the data file that is not stored in the working directory, provide a complete path of the file, such as.

read.table("d:/data.dat" , header = TRUE)
read.table("d:/Rdata/data.txt" , header = TRUE)

Note that read.table() is used to read the data from external files that have normally a special form:

  • The first line of the file should have a name for each variable in the data frame. However, if the first row does not contain the name of a variable then the header argument should not be set to FALSE.
  • Each additional line of the file has its first item a row label and the values for each variable.

In R it is strongly suggested that variables need to be held in the data frame. For this purpose read.table() function in R can be used. For further details about read.table() function use,

help(read.table)
read.table function in R; rfaqs.com

Important Arguments of read.table Function:

  • file: (required argument) it is used to specify the path to the file one wants to read.
  • header: A logical value (TRUE or FALSE) indicating whether the first line of the file contains column names. The default value is set to FALSE.
  • sep: The separator that segregates values between columns. The default is set to white space. One can specify other delimiters like commas (“,”) or tabs (“\t”).
  • as.is: A vector of logical values or column indices specifying which columns to read as characters and prevent conversion to numeric or factors.
  • colClasses: A vector specifying the data type for each column. Useful for ensuring specific data formats during import. This can be useful to ensure the data is read in the correct format (e.g., numeric, character).
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Plot Function in R

This article about the plot function in R Language gives some introduction about the plot() function, the use and purpose of its arguments, and a few examples are provided. Using the R plot function one can draw different graphical representations and the arguments of the plot() function can be used to enhance the graph.

Introduction to Graphics in R Language

Question: Can we draw graphics in R language?
Answer: Yes. R language produces high-quality statistical graphs. There are many useful and sophisticated kinds of graphs available in R.

Question: Where graphics are displayed in R?
Answer: In R, all graphs are produced in a window named Graphic Windows which can be resized.

Question: What is the use of the plot function in R?
Answer: In R, plot() is a generic function that can be used to make a variety of point and line graphs. plot() function can also be used to define a coordinate space.

Important Arguments of the Plot Function in R

Question: What are the arguments of the plot() function?
Answer: There are many arguments used in the plot() function. Some of these arguments are x, y, type, xlab, ylab, etc. To see the full list of arguments of the plot() write the command in the R console;

args(plot.default)

Question: Are all arguments necessary to be used in R?
Answer: No. The first two arguments x and y provide the horizontal and vertical coordinates of points or lines to be plotted and define a data-coordinate system for the graph. At least argument x is required. Note that many of the arguments are set to default values in the plot function.

Question: What is the use of the argument type in the plot() function?
Answer: In the R plot function, the argument type determines the type of the graph to be drawn. Several types of graphs can be drawn. The default type of graph type=’p’, plots points at the coordinates specified by the x and y argument. Specifying type=’l’ produces a line graph, and type=’n’ sets up the plotting region to accommodate the data set but plots nothing.

Other Types of Graphs: Setting type Argument

Question: Are there other types of graphs?
Answer: Yes. Setting type=’b’, draw graphs having both points and lines. Setting type=’h’ draws histogram-like vertical lines and setting type=’s’ and type=’S’ draws stair-step-like lines starting horizontally and vertically respectively.

Question: What is the use of xlim and ylim in plot() function?
Answer: The arguments xlim and ylim may be used to define the limits of the horizontal and vertical axes. Usually, these arguments are unnecessary, because R language reasonably picks limits from x and y.

Question: What are the purpose of xlab and xlab arguments in the plot() function?
Answer: xlab and ylab argument tack character-string arguments to label the horizontal and vertical axes.

Examples of R Plot Function in R

Question: Provide a few examples of the R plot function.
Answer: The following are a few examples of R plot functions. Suppose you have a data set on variables x and y, such as

x <- rnorm(100, m=10, sd=10)
y <- rnorm(100)

plot(x, y)
plot(x, y, xlab='X  (Mean=10, SD=10)',   ylab='Y (Mean=1, SD=1)' , type='l')
plot(x, y, xlab='X  (Mean=10, SD=10)',   ylab='Y (Mean=1, SD=1)' , type='o')
plot(x, y, xlab='X  (Mean=10, SD=10)',   ylab='Y (Mean=1, SD=1)' , pch=10)
Introduction to plot function in R

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Objects in R Language: Secrets

The post is about objects in R Language. In R everything is an object. The commands run in a session can be saved or loaded in a file as history.

Loading Saved Work

Question 1: How can I retrieve (load) the saved work using the history function in R?
Answer: The loadhistory() function will load an “.Rhistory” file.

loadhistory("d:/file_name.Rhistory")

This function will load the file named “file_name.Rhistory” from D: drive.

The other way may be to access the “.Rhistory” file through the file menu. For this click File and then Load History. From the dialog box, browse the folder where you saved the “.Rhistory” file and click open to start working.

Script File in R

Question 2: How do I use a script of commands and functions saved in a text file?
Answer: The script of commands and functions saved in a text file (also called a script file) can be used to write the following command.

source("d:/file_name.txt")

The “file_name.txt” will load from D: drive.

Question 3: How do I get R to echo back the R commands and functions in a script file that I am sourcing into R? That is, the functions that I have written, I want to see these functions are being executed.
Answer: use echo=TRUE argument by using source() function

source("d:/file_name.txt", echo = T)

Question 4: How do I close the help file when working on a Macintosh operating system?
Answer: Typing just q will close the help file and bring you back to the R console.

Objects in R Language: Currently Available Objects

Question 5: How can I see a list of currently available objects in R?
Answer: Use the objects() or ls() functions to see the list of objects currently available

objects()
ls()
Objects in R Language

Remove Objects and Functions

Question 6: How do I remove/delete unwanted objects and functions?
Answer: The rm() function can be used to delete or remove the objects that are not required. The commands below will delete objects named object_name1 & object_name2 and functions named function_name1 & function_name2.

rm(object_name1, object_names2)
rm(function_name1, function_name2)

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