#
# Unit 8 - Data frames 
#
# Scanning a data frame 
#

# Loading data 
# Notice this .csv includes NAs 
setwd("c:/R")
employees <- read.csv("employeesNA.csv")
print(employees)


# Problem 1 
# Set all salaries as 20000. 
employees$SALARY <- 20000
print(employees[employees$GENDER == 2,])
print(employees)


# Problem 2: 
# Produce a vector including all 
# names of types of columns in 
# the data frame employees. 
print(class(employees$ID))
print(class(employees$FNAME))


# Scanning columns directly 

# What about this? 
for (col in employees) {
  print(col)
}


# Solution to Problem 1 
types <- c() 
for (col in employees) {
  types <- c(types, class(col))
}
print(types)



# Problem 3: 
# Produce a vector including all indices of 
# columns of type integer. 
indices <- c() 
for (col in employees) {
  if (class(col) == "integer") 
    indices <- c(indices, ??)
  }
}
print(types)


# Scanning column indices 

# Reminder: data frame's 
# dimensions and indices 
print(employees)
print(ncol(employees))

# What does this code produce? 
inds <- 1:ncol(employees)
print(inds)


# What does this code print? 
for (ind in 1:ncol(employees)) {
  print(ind)
}

# and this? 
for (ind in 1:ncol(employees)) {
  print(employees[,ind])
}

# and this? 
for (ind in 1:ncol(employees)) {
  print(employees[,ind])
}


# Solution to Problem 3
indices <- c() 
for (ind in 1:ncol(employees)) {
  if (class(employees[,ind]) == "integer") {
    indices <- c(indices, ind) 
  }
}
print(indices)
print(employees)
print(class(employees$SALARY))



# Problem 4
# Produce a vector including 
# all last names of persons 
# about whom at least one detail 
# is missing. 

employees <- read.csv("employeesNA.csv")
print(employees)


# Scanning row indices 

# What does this code produce? 
inds <- 1:nrow(employees)
print(inds)

# And this? 
for (ind in 1:nrow(employees)) {
  print(ind)
}

# What does this code print?
for (ind in 1:nrow(employees)) {
  print(employees[ind,])
}



# And this?
for (i in 1:nrow(employees)) {
  print(employees[i,])
}


# Solution to problem 4. 
indices <- c() 
for (ind in 1:nrow(employees)) {
  df <- employees[ind,]
  found <- FALSE
  for (col in df) {
    if (is.na(col[1])) {
      found <- TRUE
    }
  }
  if (found) {
    indices <- c(indices, ind)
  }
}
print(indices)
print(employees)