Functions exercises vol. 2: solutions

####################
#                  #
#    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. 

Id=rep(c(1,2,3,4),each=3)
Letter=rep(letters[1:3],4)
x=seq(1,43,along.with=Id)
y=seq(-20,0,along.with=Id)
M=data.frame(Id,Letter,x,y)

ADD_COL=function(M,v)
{
  if(nrow(M)==length(v))
    M=cbind(M,v)
  return(M)
}

z=seq(1,100,along.with=Id)
M=ADD_COL(M,z)

u=c(1:10)
M=ADD_COL(M,u)


w=seq(0,20,along.with=Id)
M=ADD_COL(M,w)

M

####################
#                  #
#    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']

change=function(df,a,b)
{
  aux=df[a,'Code']
  df[a,'Code']=df[b,'Code']
  df[b,'Code']=aux
  return(df)
}

df=change(df,1,3)
df=change(df,7,2)
df=change(df,5,10)
df

####################
#                  #
#    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:
#  sum(x*df[1:i,1])+sum(y*df[1:i,2])

A=c(1:10)
B=seq(100,10,-10)
H=seq(-200,-50,along.with=B)
df=data.frame(A,B,H)

NEWDF=function(df,x,y)
{
  for (i in 1:nrow(df))
    df[i,4]=sum(x*df[1:i,1])+sum(y*df[1:i,2])
names(df)[4]=paste('SUM',x,y,sep='_')
df
}

NEWDF(df,3,6)

NEWDF(df,7,5)

####################
#                  #
#    Exercise 4    #
#                  #
####################
#Create a function that given a numeric vector, sort this in ascending order and duplicate it by two.

FUNVector1=function(v)
{
  v=sort(v)*2
  return(v)
}
v=c(2,4,1,7,3,2,7,9)
FUNVector1(v)

####################
#                  #
#    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 <code>w="a" "v" "7" "4" "q"</code> , the function will return <code>w=8 14</code>.

FUNVector2=function(w)
{
  w=as.numeric(w[-which(w %in% letters)])
  w
  w=FUNVector1(w)
  return(w)
}
a=c('a','v',4,7,'q')
a=FUNVector2(a)
a

b=c(letters[1:23],10:1,letters[24:26],11:22)
b=FUNVector2(b)
b

####################
#                  #
#    Exercise 6    #
#                  #
####################
# Create a function that given a string 
# ST='NAME: Maria /COUNTRY:uruguay /EMAIL: mariaUY@gmail.com'
# return a data.frame
#      [,1]      [,2]              
# [1,] "NAME"    " Maria "         
# [2,] "COUNTRY" "uruguay "        
# [3,] "EMAIL"   " mariaUY@gmail.com"
# 
ST='NAME: Maria /COUNTRY:uruguay /EMAIL: mariaUY@gmail.com'
DF=function(ST)
{
A=unlist(strsplit(ST,'/'))
M=rbind(unlist(strsplit(A[1],':')),unlist(strsplit(A[2],':')),unlist(strsplit(A[3],':')))
return(M)
}
M=DF(ST)
M

####################
#                  #
#    Exercise 7    #
#                  #
####################
# Consider a vector:
 ST=c('NAME:Maria /COUNTRY:uruguay /EMAIL:mariaUY@gmail.com','NAME:Paul/COUNTRY:UK /EMAIL:PaulUK@gmail.com','NAME:Jhon /COUNTRY:USA /EMAIL:JhonUSA@gmail.com','NAME:Carlos /COUNTRY:Spain /EMAIL:CarlosSP@gmail.com')

# 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"   "mariaUY@gmail.com" "PaulUK@gmail.com" "JhonUSA@gmail.com" "CarlosSP@gmail.com"

ST=c('NAME:Maria /COUNTRY:uruguay /EMAIL:mariaUY@gmail.com','NAME:Paul/COUNTRY:UK /EMAIL:PaulUK@gmail.com','NAME:Jhon /COUNTRY:USA /EMAIL:JhonUSA@gmail.com',
     'NAME:Carlos /COUNTRY:Spain /EMAIL:CarlosSP@gmail.com')
DF2=function(V)
{
  M=DF(V[1])
  for (i in 2:length(V))
    M=cbind(M,DF(V[i])[,2])
  return(M)
}
DF2(ST)

####################
#                  #
#    Exercise 8    #
#                  #
####################
#Create a function that given a numeric vector X returns the digits 0 to 9 that are not in X

DIGITS=function(X)
{
  b=0:9
  Y=b[!b%in%a]
  return(Y)
}
a=c(1,5,3,8)
DIGITS(a)

####################
#                  #
#    Exercise 9    #
#                  #
####################
#Create a function that given two strings, check if one is an anagram of another.
library('stringr')