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

# Loading data 
setwd("c:/R")
gradesWide <- read.csv("grades.csv")
print(gradesWide)

# TRANSPOSING

# Transposing a data frame 
transposedDF <- t(gradesWide)
print(transposedDF)
print(class(transposedDF))
transposedDF <- data.frame(transposedDF)
print(class(transposedDF))
print(transposedDF)


# WIDE FORMAT TO LONG FORMAT

gradesWide <- read.csv("grades.csv")
print(gradesWide)

# Required library
library(reshape2)
# Wide to long
gradesLong <- melt(gradesWide, 
                   id.vars = c("CODE", "ID"), 
                   variable.name = "YEAR",
                   value.name = "GRADE")
print(gradesLong)


# long to wide
gradesWide <- dcast(gradesLong, 
                    CODE + ID ~ YEAR, 
                    value.var = "GRADE")
print(gradesWide)


# IMPORTANT: avoid including additional columns 
# in the covnerted data frame
gradesWide <- read.csv("grades.csv")
gradesWide$AVERAGE <- (gradesWide$YEAR1 + gradesWide$YEAR2 + gradesWide$YEAR3) / 3
print(gradesWide)
gradesLong <- melt(gradesWide, 
                   id.vars = c("CODE", "ID"), 
                   variable.name = "YEAR",
                   value.name = "GRADE")
print(gradesLong)


# See also: tidyr's gather(), among others