###QUESTION 10

###Topic: Sheet 8 Exercise 1
###Question: I dont really understand this components:

y<- c()
#and then further is y<- c(y, names(data)[i])

myfact <-  function(data) {
  y <-c()
  for (i in 1:dim(data)[2]){
    if (is.factor(data[,i]) == TRUE){
      y<-c(y, names(data)[i])
    }
  }
  return(y)
}

heartbeats <- read.table("C:/Users/Ingo/Documents/A-Uni/EES/3rd_semester/Rcourse2020_Tutoring/data/heartbeats.txt")
myfact(heartbeats)

## NULL

ht2 <- heartbeats
ht2$wghtcls <- as.factor(ht2$wghtcls)
myfact(ht2)

## [1] "wghtcls"

#my confusion is mostly why do I need to put y inside the vector?
#I can see is necessary because I tried doing it without it and it didnt work,
#but I still dont understand it. And also:
#  We have to define that "y" variable as a vector, because it can be multiple elements right?


###Answer:
#maybe it becomes more clear with a simpler example.
#here we will simply add a new number to the end of a vector

x <- c()

for (i in 1:5) {
  x <- c(x, i)
}

#First we need to define x, because in our for loop, we already attempt to assign x to something
#even though it doesn't exist yet.
#if you'd run the code:

# clean your R environment to remove x
rm(list=ls())

#for (i in 1:5) {
#  x <- c(x, i)
#  print(x)
#}

#without creating x first, you would get an error saying "Object 'x' not found

#What you`re doing in the code and the reason why x (or y in the example above) is inside the vector is that the
#new value will be added to the end, instead of just overwriting the previous one.
#if you print the x after each iteration you see that the current value of i gets added to the end of the vector
x <- c()

for (i in 1:5) {
  print(x)
  x <- c(x, i)
}

## NULL
## [1] 1
## [1] 1 2
## [1] 1 2 3
## [1] 1 2 3 4

print(x)

## [1] 1 2 3 4 5

#if the current value of x weren't in the assignment, you'd just overwrite x every round

x <- c()

for (i in 1:5) {
  print(x)
  x <- c(i)
}

## NULL
## [1] 1
## [1] 2
## [1] 3
## [1] 4

print(x)

## [1] 5

#depending on what you will do with the variable, you don't necessarily have to define it as a vector,
#you can also assign x to be NULL it will become a vector in the for loop anyway

x <- NULL

for (i in 1:5) {
  print(x)
  x <- c(x, i)
}

## NULL
## [1] 1
## [1] 1 2
## [1] 1 2 3
## [1] 1 2 3 4

print(x)

## [1] 1 2 3 4 5

#if you first define x as having a specific value (e.g. NA or 0) then this will actually be the first entry

x <- NA

for (i in 1:5) {
  print(x)
  x <- c(x, i)
}

## [1] NA
## [1] NA  1
## [1] NA  1  2
## [1] NA  1  2  3
## [1] NA  1  2  3  4

print(x)

## [1] NA  1  2  3  4  5