TVORBA DATOVÝCH OBJEKTŮ A MANIPULACE S NIMI

Vít Gabrhel

vit.gabrhel@mail.muni.cz

FSS MU,

25. 9. 2017

Harmonogram

 0. Rekapitulace předchozí hodiny

 1. Vector

 2. Matrix

 3. Factor

 4. Data Frame

Co je to objekt?

Vector

Vector je jednoduchý datový objekt o různé délce obsahující hodnoty

• c("Reservoir Dogs", "Pulp Fiction", "Inglorious Basterds")
• c(421, 469, 51)
• c(421, "Reservoir Dogs", "death", FALSE, 10)

 Počet cursing words dle filmů

• Words_Movie = c(421, 469, 57, 51)

 Co je co aneb pojmenování   vektorů

• names(Words_Movie) = c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds")

 Vektorová aritmetika

 Sčítání vektorů

• Hell = c(12, 5, 3, 4)
• Goddamn = c(10, 28, 7, 8)
• Spirituality = Hell + Goddamn

Součet hodnot ve vektoru

• Words_N <- sum(Spirituality)

 Výběr hodnot(y) z vektoru

•  Words_Movie[c(1, 4)]
•  Words_Movie[c("Reservoir Dogs", "Inglorious Basterds")]

Vector

Logické operátory

 < for less than
 > for greater than
 <= for less than or equal to
 >= for greater than or equal to
 == for equal to each other
 != not equal to each other​

Zaznívalo ve filmech více slovo "Hell" nebo "Goddamn"?

• Hell < Goddamn

 Porovnání hodnot(y) mezi vektory

• names(Hell) = c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds")
  names(Goddamn) = c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds")
• Hell[c(1, 4)] > Goddamn[c(1, 4)]
• Hell[c("Reservoir Dogs", "Inglorious Basterds")] != Goddamn[c("Reservoir Dogs", "Inglorious Basterds")]
• names(Spirituality) = c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds")
• PulpFiction_Celkem <- Spirituality[c(2)] > 50

Ve kterých filmech padlo více cursing words, než byl jejich průměrný počet za osm filmů?

• Words_Movie > 213

Factor

Filmy = c("Kill Bill 1", "Reservoir Dogs", "Inglorious Basterds", "Pulp Fiction")

class(Filmy)

Nominální kategorie

Factor_Filmy = as.factor(Filmy)

class(Factor_Filmy)

levels(Factor_Filmy) <- c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds")

 

Ordinalizace

Factor_Filmy <- factor(Filmy, order = TRUE, levels = c("Reservoir Dogs", "Pulp Fiction", "Kill Bill 1", "Inglorious Basterds"))

Matrix

In R, a matrix is

• a collection of elements of the same data type (numeric, character, or logical)
• arranged into a fixed number of rows and columns.
• Since you are only working with rows and columns, a matrix is called two-dimensional.

You can construct a matrix in R with the matrix() function. Consider the following example:

• matrix(1:9, byrow = TRUE, nrow = 3)

The first argument is the collection of elements that R will arrange into the rows and columns of the matrix. Here, we use 1:9 which is a shortcut for c(1, 2, 3, 4, 5, 6, 7, 8, 9).

The argument byrow indicates that the matrix is filled by the rows. If we want the matrix to be filled by the columns, we just place byrow = FALSE.

 

The third argument nrow indicates that the matrix should have three rows.

• Analogicky "ncol"

Matrix

O cursing words v Tarantinových filmech už něco víme. Co ale počet mrtvých?

 

Budeme se věnovat Pulp Fiction, Inglorious Basterds a Django Unchained spolu s počtem zesnulých postav. Přidáme k tomu známý počet cursing words v příslušných filmech: 

• Pulp_Fiction = c(7, 469)
• Inglorious_Basterds = c(48, 58)
• Django_Unchained = c(47, 262)

 

Filmy <- matrix(c(Pulp_Fiction, Inglorious_Basterds, Django_Unchained), nrow = 3, byrow = TRUE)

View(Filmy)

Pojmenování řádků/sloupců

rownames(Filmy) <- c("Pulp_Fiction", "Inglorious_Basterds", "Django_Unchained")
colnames(Filmy) <- c("Deaths", "Words")

View(Filmy)

Matrix

Death_Curse = c(7, 48, 47, 469, 58, 262)
Death_Curse_Matrix = matrix(Death_Curse, nrow = 3, byrow = FALSE,
dimnames = list(c("Pulp_Fiction", "Inglorious_Basterds", "Django_Unchained")))

colnames(Death_Curse_Matrix) <- c("Deaths", "Curses")

colSums(Death_Curse_Matrix)

 

Jak do matice přidat sloupec / řádek?

Skrze příkaz cbind() / rbind()

 

Filmy si rozdělíme z hlediska období tvorby (90s, 00s a 10s) s kódy "0", "1" a "2":

 

Period = c(0, 1, 2)
Period_Matrix = matrix(Period)
rownames(Period_Matrix) = c("90s", "00s", "10s")

colnames(Period_Matrix) <- c("Period")

 

Death_Curse_Period = cbind(Death_Curse_Matrix, Period_Matrix)
Death_Curse_Period  

Matrix

 Jak příkazem zjistit aktivní objekty?

 ls()

 

 Jak vybrat konkrétní prvky z matice?

 Similar to vectors, you can use the square brackets [ ] to select one or multiple elements  from a matrix.

• Whereas vectors have one dimension, matrices have two dimensions. You should therefore use a comma to separate that what to select from the rows from that what you want to select from the columns. For example:
  • Death_Curse_Period[1,2] selects the element at the first row and second column.
  • Death_Curse_Period[1:3,2:3] results in a matrix with the data on the rows 1, 2, 3
    and columns 2 and 3.
• If you want to select all elements of a row or a column, no number is needed before
  or after the comma, respectively:
  • Death_Curse_Period[,1] selects all elements of the first column.
  • Death_Curse_Period[1,] selects all elements of the first row.

 

Matrix

Jaký byl průměrný počet mrtvých ve sledovaných filmech?
Mean_Dead = Death_Curse_Period[,1]
mean(Mean_Dead)

 

Jaký je Tarantino index (tj. počet mrtvých na počet nadávek) pro Inglorious Basterds?
Dead_Curse = data.frame(Death_Curse_Period[2,1:2])

Dead_Curse[2,1]/Dead_Curse[1,1]

Data Frame

Data Frame je matice tak, jak ji chápeme při analýze dat

• A data frame has the variables of a data set as columns and the observations as rows

V čem se v R "Data Frame" liší od "Matrix"?

• All the elements that you put in a matrix should be of the same type

Data Frame

Vyvolání Data Frame z R

 data()
 data(USArrests)

 View(USArrests)

 ??USArrests

Jak se zorientovat v Data Frame?

• head() - show the first observations of a data frame
• tail() - prints out the last observations in your data set
• str() - struktura dat

Data Frame

Tvorba vlastní Data Frame

 data.frame()

# Planety - definování vektorů

• 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)

 

# Planety

• Planets = data.frame(name, type, diameter, rotation, rings)

# Struktura dat

• str(Planets)
• head(Planets)
• tail(Planets)

Data Frame

 Výběr prvků

• Planets[1:3,1]
• Planets[1:3,"name"]
• Planets$name
• Planets[rings, "name"]

 Subsoubory

• subset(Planets, subset = rings)
• subset(Planets, subset = (diameter < 4))

 Seřazování

• order(Planets$diameter)
• Planets[order("diameter")]

Zdroje

Cornelissen, J. (n.d.) Introduction to R. Dostupné online na:
https://www.datacamp.com/courses/free-introduction-to-r

Cvičení

Zadání