--5-Data frames

#1-What's a data frame?

#Click 'Submit Answer'. 
#The data from the built-in example data frame mtcars 
#will be printed to the console.
datasets::mtcars

# Print out built-in R data frame
mtcars

#2-Quick, have a look at your data set

# Call head() on mtcars
head(mtcars)

#3-Have a look at the structure

# Investigate the structure of mtcars
str(mtcars)
class(mtcars)
attributes(mtcars)

#4-Creating a data frame

#Use the function data.frame() to construct a data frame. 
#Pass the vectors name, type, diameter, rotation and rings 
#as arguments to data.frame(), in this order.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", 
"Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", 
          "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

#5-Creating a data frame (2)

# Use str() to investigate the structure of the new planets_df variable.
# Check the structure of planets_df in no #4-Creating a data frame 
str(planets_df)

#6-Selection of data frame elements

#From planets_df, select the diameter of Mercury: 
#this is the value at the first row and the third column. 
#Simply print out the result.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter",
 "Saturn", "Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant",
           "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

# Print out diameter of Mercury (row 1, column 3)
planets_df[1,3]

# Print out data for Mars (entire fourth row)
planets_df[4,]

#7-Selection of data frame elements (2)

#Select and print out the first 5 values in the "diameter" 
#column of planets_df.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", 
"Saturn", "Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", 
          "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

# Select first 5 values of diameter column
planets_df[1:5,"diameter"]

#8-Only planets with rings

#Use the $ sign to select the rings variable from planets_df. 
#Store the vector that results as rings_vector.
#Print out rings_vector to see if you got it right.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", 
"Saturn", "Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", 
          "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

# Select the rings variable from planets_df
rings_vector <- planets_df$rings

# Print out rings_vector
rings_vector

#9-Only planets with rings (2)

#The code on the right selects the name column of all planets 
#that have rings. 
#Adapt the code so that instead of only the name column, 
#all columns for planets that have rings are selected.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", 
"Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet",
 "Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", "Gas giant",
           "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

# Select the rings variable from planets_df
rings_vector <- planets_df$rings

# Print out rings_vector
rings_vector

# Adapt the code to select all columns for planets with rings
planets_df[rings_vector,]

#10-Only planets with rings but shorter

#Use subset() on planets_df to select planets that have 
#a diameter smaller than Earth.
#Because the diameter variable is a relative measure of 
#the planet's diameter
#w.r.t that of planet Earth, your condition is diameter < 1.

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn",
 "Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", 
          "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

# Select planets with diameter < 1
subset(planets_df,subset=diameter<1)

#11-Sorting

#Experiment with the order() function in the console. 
#Click 'Submit Answer' when you are ready to continue.
# Play around with the order function in the console

cevi<-c(10,100,9)
order(cevi)
cevi[order(cevi)]

#12-Sorting your data frame

#Call order() on planets_df$diameter in no #4
#(the diameter column of planets_df). Store the result as positions.
#Now reshuffle planets_df with the positions vector as row indexes 
#inside square brackets. Keep all columns. Simply print out the result.
# planets_df is pre-loaded in your workspace
# Use order() to create positions

# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter",
 "Saturn", "Uranus",
 "Neptune")
type <- c("Terrestrial planet", "Terrestrial planet", 
"Terrestrial planet", 
          "Terrestrial planet", "Gas giant", "Gas giant", 
          "Gas giant", "Gas giant")
diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67)
rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)

# Create a data frame from the vectors
planets_df <-data.frame(name,type,diameter,rotation,rings)
planets_df

positions <-  order(planets_df$diameter)

# Use positions to sort planets_df
planets_df[positions,]