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Answers to the exercises are available here.

Exercise 1

Create a function that given a data frame and a vector, will add a the vector (if the vector length match with the rows number of the data frame)
as a new variable to the data frame.

Exercise 2

Consider a data frame df:
 Id=c(1:10) Age=c(14,12,15,10,23,21,41,56,78,12) Sex=c('F','M','M','F','M','F','M','M','F','M') Code=letters[1:10] df=data.frame(Id,Age,Sex,Code) 

Create a function that, given a data frame and two indexes, exchanges two values ​​of the Code variable with each other.
For example, if the index is 1 and 3, you assign:
 df[1,'Code']=df[3,'Code'] df[3,'Code']=df[1,'Code'] 

Exercise 3

Consider two variables x,y and a data frame df:
 x,y integer A=c(1:10) B=seq(100,10,-10) H=seq(-200,-50,along.with=B) df=data.frame(A,B,H) 

Create a function that given a data frame df calculate a new variable ‘SUM_x_y'(If x=2 and y=3, then the new variable will be ‘SUM_2_3’,
if x=4 and y=10, then the new variable will be ‘SUM_4_10’),such that for each row ‘i’ is equal to:
 sum(x*df[1:i,1])+sum(y*df[1:i,2]) 

Exercise 4

Create a function that given a numeric vector, sort this in ascending order and duplicate it by two.

Exercise 5

Create a function that given a vector alpha numeric, keep only the numbers and apply the function created on exercise 4.
For example, if the input is a vector w="a" "v" "7" "4" "q" , the function will return w=8 14.

Exercise 6

Create a function that given a string
 ST='NAME: Maria /COUNTRY:uruguay /EMAIL: [email protected]' 
return a matrix
 [,1] [,2] [1,] "NAME" " Maria " [2,] "COUNTRY" "uruguay " [3,] "EMAIL" " [email protected]" 

Exercise 7

Consider a vector:
 ST=c('NAME:Maria /COUNTRY:uruguay /EMAIL:[email protected]','NAME:Paul/COUNTRY:UK /EMAIL:[email protected]', 'NAME:Jhon /COUNTRY:USA /EMAIL:[email protected]','NAME:Carlos /COUNTRY:Spain /EMAIL:[email protected]') 

Create a function that given a vector string ST return a matrix:
 [,1] [,2] [,3] [,4] [,5] [1,] "NAME" "Maria " "Paul" "Jhon " "Carlos " [2,] "COUNTRY" "uruguay " "UK " "USA " "Spain " [3,] "EMAIL" "[email protected]" "[email protected]" "[email protected]" "[email protected]" 

Exercise 8

Create a function that given a numeric vector X returns the digits 0 to 9 that are not in X. If X=0 2 4 8
the function return 1 3 5 6 7 9

Exercise 9

Create a function that given two strings (one word each), check if one is an anagram of another.

Exercise 10
Create a function that given one word, return the position of word’s letters on letters vector.
For example, if the word is ‘abc’, the function will return 1 2 3.

Want to practice functions a bit more? We have more exercise sets on this topic here.