#
# Practice 1
#

# option 1 - convenient step-by-step way

name <- c("Jose","Sara","Maria","Frank","John")
age <- c(17,22,21,21,18)
sex <- c("male","female","female","male","male")
econ_scale <- c(-3,0.6,2,-3,3.1)
soc_scale <- c(-7.2,0.2,0,0.5,3)

practice1_df <- data.frame(name, age, sex, econ_scale, soc_scale)

str(practice1_df)

# option 2 - one-command way

practice1_df <- data.frame(name = c("Jose","Sara","Maria","Frank","John"),
                           age = c(17,22,21,21,18),
                           sex = c("male","female","female","male","male"),
                           econ_scale = c(-3,0.6,2,-3,3.1),
                           soc_scale = c(-7.2,0.2,0,0.5,3)
)

#
# Practice 2
#

install.packages("psych")

library("psych")

dim(practice1_df)

head(practice1_df)

str(practice1_df)

describe(practice1_df) # it throws some errors at us. Not all errors are wrong. These errors are useful, as they warn us about the character class of variables "name" and "sex". It's not a bug, it's a feature.

#
# Practice 3
#

# Load a default dataset called “eurodist” / Visually inspect the data source

eurodist

# Figure out the type of the data source

str(eurodist)

class(eurodist)

# Transform data source to most suitable format for data manipulation

as.matrix(eurodist)

ed.matrix <- as.matrix(eurodist) # don't forget, you always have to save the result = create new object in the environment

#
# Practice 4
#

# Create a matrix with following parameters
# 6 by 6 layout
# Contains numbers 0 and 1 in a 0 1 0 1 0 1 0 1 pattern
# The pattern is organized by rows

# option 1 - the most transparent approach

size <- 6 * 6 # create the size object

pattern <- c(0,1) # create the repeating pattern

pattern.length <- length(pattern) # get the number of elements in the repeating pattern (length)

repetitions <- size/pattern.length # get the number of pattern repetitions

help(rep) # get the list of arguments in the rep() function

mat.data <- rep(pattern,times = repetitions) # create the matrix pattern

matrix(data = mat.data,nrow = 6,ncol = 6) # create the matrix. Oops - it is organized by columns, not by rows

matrix(data = mat.data,nrow = 6,ncol = 6,byrow = TRUE) # use the argument "byrow" to change the direction

result.matrix <- matrix(data = mat.data,nrow = 6,ncol = 6,byrow = TRUE) # save result in the environment

# option 2 - the lazy/proficient approach

matrix(data = rep(x = c(0,1),18),nrow = 6, ncol = 6, byrow = TRUE)

result.matrix <- matrix(data = rep(x = c(0,1),18),nrow = 6, ncol = 6, byrow = TRUE)