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2 R Tutorial Programming

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Part 2 - R programming Tutorial for beginners - Programming basics.

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2 R Tutorial Programming

  1. 1. R Programming Sakthi Dasan Sekar
  2. 2. R Programming Operators R has many operators to carry out different mathematical and logical operations. Operators in R can be classified into the following categories.  Arithmetic operators  Relational operators  Logical operators  Assignment operators http://shakthydoss.com 2
  3. 3. R Programming Arithmetic Operators Arithmetic operators are used for mathematical operations like addition and multiplication. Arithmetic Operators in R Operator Description + Addition - Subtraction * Multiplication / Division ^ Exponent %% Modulus %/% Integer Division http://shakthydoss.com 3
  4. 4. R Programming Relational operators Relational operators are used to compare between values. Relational Operators in R Operator Description < Less than > Greater than <= Less than or equal to >= Greater than or equal to == Equal to != Not equal to http://shakthydoss.com 4
  5. 5. R Programming Logical Operators Logical operators are used to carry out Boolean operations like AND, OR etc. Logical Operators in R Operator Description ! Logical NOT & Element-wise logical AND && Logical AND | Element-wise logical OR || Logical OR http://shakthydoss.com 5
  6. 6. R Programming Assignment operator Assigment operators are used to assign values to variables. Variables are assigned using <- (although = also works) age <- 18 (left assignment ) 18 -> age (right assignment) http://shakthydoss.com 6
  7. 7. R Programming if...else statement Syntax if (expression) { statement } If the test expression is TRUE, the statement gets executed. The else part is optional and is evaluated if test expression is FALSE. age <- 20 if(age > 18){ print("Major") } else { print(“Minor”) } http://shakthydoss.com 7
  8. 8. R Programming Nested if...else statement Only one statement will get executed depending upon the test expressions. if (expression1) { statement1 } else if (expression2) { statement2 } else if (expression3) { statement3 } else { statement4 } http://shakthydoss.com 8
  9. 9. R Programming ifelse() function ifelse() function is nothing but a vector equivalent form of if..else. ifelse(expression, yes, no) expression– A logical expression, which may be a vector. yes – What to return if expression is TRUE. no – What to return if expression is FALSE. a = c(1,2,3,4) ifelse(a %% 2 == 0,"even","odd") http://shakthydoss.com 9
  10. 10. R Programming • For Loop For loop in R executes code statements for a particular number of times. for (val in sequence) { statement } vec <- c(1,2,3,4,5) for (val in vec) { print(val) } http://shakthydoss.com 10
  11. 11. R Programming While Loop while (test_expression) { statement } Here, test expression is evaluated and the body of the loop is entered if the result is TRUE. The statements inside the loop are executed and the flow returns to test expression again. This is repeated each time until test expression evaluates to FALSE. http://shakthydoss.com 11
  12. 12. R Programming break statement A break statement is used inside a loop to stop the iterations and flow the control outside of the loop. num <- 1:5 for (val in num) { if (val == 3){ break } print(val) } output 1, 2 http://shakthydoss.com 12
  13. 13. R Programming next statement A next statement is useful when you want to skip the current iteration of a loop alone. num <- 1:5 for (val in num) { if (val == 3){ next } print(val) } output 1,2,4,5 http://shakthydoss.com 13
  14. 14. R Programming repeat loop A repeat loop is used to iterate over a block of code multiple number of times. There is no condition check in repeat loop to exit the loop. You must specify exit condition inside the body of the loop. Failing to do so will result into an infinite looping. repeat { statement } http://shakthydoss.com 14
  15. 15. R Programming switch function switch function is more like controlled branch of if else statements. switch (expression, list) switch(2, "apple", “ball" , "cat") returns ball. color = "green" switch(color, "red"={print("apple")}, "yellow"={print("banana")}, "green"={print("avocado")}) returns avocado http://shakthydoss.com 15
  16. 16. R Programming scan() function scan() function helps to read data from console or file. reading data from console x <- scan() Reading data from file. x <- scan("http://www.ats.ucla.edu/stat/data/scan.txt", what = list(age = 0,name = "")) Reading a file using scan function may not be efficient way always. we will see more handy functions to read files in upcoming chapters. http://shakthydoss.com 16
  17. 17. R Programming Running R Script The source () function instructs R reads the text file and execute its contents. source("myScript.R") Optional parameter echo=TRUE will echo the script lines before they are executed source("myScript.R", echo=TRUE) http://shakthydoss.com 17
  18. 18. R Programming Running a Batch Script R CMD BATCH command will help to run code in batch mode. $ R CMD BATCH myscript.R outputfile In case if you want the output sent to stdout or if you need to pass command- line arguments to the script then Rscript command can be used. $ Rscript myScript.R arg1 arg2 http://shakthydoss.com 18
  19. 19. R Programming Commonly used R functions append() Add elements to a vector. c() Combine Values into a Vector or List identical() Test if 2 objects are exactly equal. length() Returns length of of R object. ls() List objects in current environment. range(x) Returns minimum and maximum of vector. rep(x,n) Repeat the number x, n times rev(x) Reversed version of its argument. seq(x,y,n) Generate regular sequences from x to y, spaced by n unique(x) Remove duplicate entries from vector http://shakthydoss.com 19
  20. 20. R Programming Commonly used R functions tolower() Convert string to lower case letters toupper() Convert string to upper case letters grep() Used for Regular expressions http://shakthydoss.com 20
  21. 21. R Programming Commonly used R functions summary(x) Returns Object Summaries str(x) Compactly Display the Structure of an Arbitrary R Object glimpse(x) Compactly Display the Structure of an Arbitrary R Object (dplyr package) class(x) Return the class of an object. mode(x) Get or set the type or storage mode of an object. http://shakthydoss.com 21
  22. 22. R Programming Knowledge Check http://shakthydoss.com 22
  23. 23. R Programming Which of following is valid equation. A. TRUE %/% FALSE = TRUE B. (TRUE | FALSE ) & (FALSE != TRUE) == TRUE C. (TRUE | FALSE ) & (FALSE != TRUE) == FALSE D. "A" && "a" Answer B http://shakthydoss.com 23
  24. 24. R Programming 4 __ 3 = 1. What operator should be used. A. / B. * C. %/% D. None of the above Answer C http://shakthydoss.com 24
  25. 25. R Programming What will be output ? age <- 18 18 -> age print(age) A. 18 B. Error C. NA D. Binary value of 18 will be stored in age. Answer A http://shakthydoss.com 25
  26. 26. R Programming Can if statement be used without an else block. A. Yes B. No Answer A http://shakthydoss.com 26
  27. 27. R Programming A break statement is used inside a loop to stop the iterations and flow the control outside of the loop. A. TRUE B. FALSE Answer A http://shakthydoss.com 27
  28. 28. R Programming A next statement is useful when you want to skip the current iteration of a loop alone. A. FALSE B. TRUE Answer B http://shakthydoss.com 28
  29. 29. R Programming Which function should be used to find the length of R object. A. ls() B. sizeOf() C. length() D. None of the above Answer C http://shakthydoss.com 29
  30. 30. R Programming Display the Structure of an Arbitrary R Object A. summary(x) B. str(x) C. ls(x) D. None of above Answer B http://shakthydoss.com 30
  31. 31. R Programming A repeat loop is used to iterate over a block of code multiple number of times. There is no condition check in repeat loop to exit the loop. A. TRUE B. FALSE Answer A http://shakthydoss.com 31
  32. 32. R Programming what will be the output of print. num <- 1:5 for (val in num) { next break print(val) } A. Error B. output 3,4,5 C. Program runs but no output is produced D. None of the above Answer C http://shakthydoss.com 32

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