{"id":475,"date":"2018-07-16T04:41:33","date_gmt":"2018-07-16T04:41:33","guid":{"rendered":"http:\/\/itp7.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=475"},"modified":"2019-05-16T09:35:41","modified_gmt":"2019-05-16T09:35:41","slug":"r-programming-2","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/itp7\/chapter\/r-programming-2\/","title":{"rendered":"R Programming – 2"},"content":{"raw":"
\"epgp<\/a>\r\n<\/span><\/div>\r\n \r\n\r\nWriting Scripts<\/strong>\r\n\r\n \r\n

In the previous module of R programming - 1, we had studied the capabilities provide by R Environment. We had seen the use of variables, operators, data structures and datasets in R. In this module, we will study how to write programs in R. This module will cover the basic programming constructs provided by R environment. Let us begin our study by typing a simple program that performs addition calculation. The following code performs addition of subject marks of 3 different subjects. Further, it calculates the percentage and is displayed on screen.<\/p>\r\n \r\n

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Rather than typing the program in a text editor and executing it from command prompt, we can use GUI to make the tasks easier. RStudio is a free GUI available for R programming. The following is a screen shot of RStudio:<\/p>\r\n

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Figure 1: Rstudio - GUI for R programming<\/p>\r\n \r\n

As you can see in the GUI, there are 4 panels, there is an editor to type the programs, the output of which is seen in console at the bottom of editor. There is also a watch windows to observe the values of variables while the programming is running. The panel provided in bottom right corner lists files of the directory, packages installed in R, it can also be used to view plots or to browse help.<\/p>\r\n \r\n\r\nDecision Making<\/strong>\r\n\r\n \r\n

As in other programming languages, R supports decision making facilities like if statements.<\/p>\r\nThe syntax of if statement is as below:\r\n

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We must be careful while using if statement, since the closing parenthesis '}' and else keyword must be in the same line. Let us see a sample program that uses decision making. The following example checks whether a number is negative or positive number and display accordingly:<\/p>\r\n

\"\"<\/p>\r\nLooping in R<\/strong>\r\n\r\n \r\n

R supports looping construct in the form of while loop and for loops. The syntax of while loop is as shown below:<\/p>\r\n

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The below code snippet display numbers from 1 to 10 using while loop. In the example, we have used the variable 'i' as looping variable.<\/p>\r\n

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The for loop iterates for definite number of values given in sequence. In the above example, we created a vector 'x' of values 1 to 8. In the above example, for loop iterated 8 times taking the assigned values one at a time. It must be noted that the for loop of R is different from that of C programming.<\/p>\r\n \r\n\r\nBreak and Next keywords<\/strong>\r\n\r\n \r\n

The break and next keywords are used in R that are similar in other programming languages. The break keyword is used to come out of loop based on certain criteria while the next keyword is used to continue execution till the criteria is met. Let us see examples that demonstrate break and next keywords. In the below code, the loop must iterate for 15 times, however, when the loop encounter value of 13, it breaks out of the loop and terminates.<\/p>\r\n

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In the following example, the loop iterates for 20 times, however, when the loop encounters the value of 13, it skips the value (does not print) and continues till the terminating criteria is satisfied.<\/p>\r\n

\"\"<\/p>\r\nWriting Interactive Programs<\/strong>\r\n\r\n \r\n

Now, let us see an interactive program where the input is given by a user. The following program checks whether a number entered by the user is prime or not. In the first line of the program, you may notice that we accept input using 'prompt()' function, the input is read using the 'readline()' function and later converted into integer using the'as.integer()' function.<\/p>\r\n \r\n

In the following program, the for loop is used differently. We have iterated the loop from value 2 upto the value 'num-1'. You may notice the syntax of for loop since it is bit different from the loop that we studied earlier in this module.<\/p>\r\n \r\n

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\"\"<\/p>\r\nReading data from files<\/strong>\r\n\r\n \r\n

Let us study how to ready data from CSV files. Suppose we have a file \"input.csv\" in the default working directory. We need to use the function \"read.csv()\" to read the data from CSV file. Further, we store the data into data frame. Each column of the data can be accessed by using '$' sign. For instance, the field with heading \"salary\" can be accessed by using the format (data$salary)<\/p>\r\n \r\n

\"\"<\/p>\r\nPlotting in R<\/strong>\r\n\r\n \r\n

R supports ploting features, such that data can be plotted from files or from data frames. R supports variety of plotting formats. The most prominent ones are as below:<\/p>\r\n\r\n