Základné operácie v R

knitr::opts_chunk$set(
  echo = TRUE,
  message = FALSE,
  warning = FALSE
)

1. Čísla

# Priradenie konštanty do premennej
a <- 15
b <- 10
a

[1] 15

b

[1] 10

# Arithmetic
sum_ab      <- a + b        # sucet
sum_ab

[1] 25

diff_ab     <- a - b        # rozdiel
diff_ab

[1] 5

prod_ab     <- a * b        # násobenie
prod_ab

[1] 150

quot_ab     <- a / b        # delenie
quot_ab

[1] 1.5

power_ab    <- a ^ b        # umocňovanie
power_ab

[1] 576650390625

mod_ab      <- b %% 4       # zbytok po delení tromi (tzv modulo)
mod_ab

[1] 2

Malé cvičenie

Vypočítajte:

\[\frac{(18^2-9)}{4}\]

(18^2 - 9) / 4

[1] 78.75

---

2. Text

first <- "Igor"                       # definovanie obsahu textovej premennej first
last  <- "Németh"                          # definovanie obsahu text. premennej last
full  <- paste(first, last)               # spojenie dvoch text. premennych do jednej (s medzerou)
full_nospace <- paste0(first, last)       # spojenie bez medzery
csv_line <- paste("jahoda", "jablko", "orech", sep = ",")  # spojenie textov s oddelovacom ,
first; last; full; full_nospace; csv_line   # bodkočiarka tu nahradzuje odskok na novy riadok 

[1] "Igor"
[1] "Németh"
[1] "Igor Németh"
[1] "IgorNémeth"
[1] "jahoda,jablko,orech"

x <- "Tenis je najlepší šport"
nchar(x) # počet znakov  v retazci "Tenis je najlepší šport"

[1] 23

x

[1] "Tenis je najlepší šport"

substr(x, 1, 13)          # podreťazec od 1. do 23. znaku

[1] "Tenis je najl"

---

3. Logické hodnoty

p <- TRUE
q <- FALSE
!p                 # NOT

[1] FALSE

p & q              # AND

[1] FALSE

p | q              # OR

[1] TRUE

xor(p, q)          # exclusive OR 

[1] TRUE

!p; !q; p & q; p | q; xor(p, q)

[1] FALSE
[1] TRUE
[1] FALSE
[1] TRUE
[1] TRUE

4. Novinka

Moja funkcia slúži na vytvorenie náhodného hesla

random_password <- function(length = 8) {
  chars <- c(letters, LETTERS, 0:9)
  paste(sample(chars, length, replace = TRUE), collapse = "")}

random_password()

[1] "Qq1gMnVP"

random_password(17)

[1] "YMo9uQ8rh75f72Heb"

Numerické vektory

Generovanie vektorov

v1 <- c(3, 5, 7, 9)
v2 <- 1:7                  
v3 <- seq(from = 0, to = 3, by = 0.75)  
v4 <- rep(7, times = 3)    
v5 <- runif(6)             
v6 <- rnorm(6)             
v1; v2; v3; v4; v5; v6

[1] 3 5 7 9
[1] 1 2 3 4 5 6 7
[1] 0.00 0.75 1.50 2.25 3.00
[1] 7 7 7
[1] 0.3233644 0.5174744 0.2200254 0.6013817 0.4882949 0.3301193
[1]  2.3771993  0.1732159 -2.7503249  0.8917910 -0.2565110 -0.2768242

Aritmetické operácie s vektormi

v <- c(2, 3, 4, 5)
v + 8           

[1] 10 11 12 13

v * 3            

[1]  6  9 12 15

(v + 3) / 2

[1] 2.5 3.0 3.5 4.0

exp(v)           

[1]   7.389056  20.085537  54.598150 148.413159

sum(c(3,5,7),c(1,1,1))          

[1] 18

crossprod(c(3,5,7),c(1,1,1))    

     [,1]
[1,]   15

c(3,5,7)*c(1,1,1)               

[1] 3 5 7

Matematické operácie s 2 vektormi rovnakého rozmeru

length(c(3,5,7,9,11))

[1] 5

length(v5)            

[1] 6

c(3,5,7,9,11) + v5    

[1]  3.323364  5.517474  7.220025  9.601382 11.488295  3.330119

Indexovanie a výber niektorych prvkov vektora

x <- c(5, 12, 3, 18, 7, 0, 21)
x[3]           

[1] 3

x[1:3]         

[1]  5 12  3

x[-4]         

[1]  5 12  3  7  0 21

x[x > 6]      

[1] 12 18  7 21

which(x > 10)  

[1] 2 4 7

Práca s chýbajúcimi hodnotami

y <- c(3, NA, 5, NA, 7)
is.na(y)

[1] FALSE  TRUE FALSE  TRUE FALSE

mean(y)                 

[1] NA

mean(y, na.rm = TRUE)   

[1] 5

Základné štatistiky a usporiadanie prvkov vektora podľa veľkosti

z <- c(12, 1, 6, 8, 10)
mean(z)                 

[1] 7.4

sd(z)                  

[1] 4.219005

max(z)                  

[1] 12

summary(z)              

   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
    1.0     6.0     8.0     7.4    10.0    12.0 

sort(z)                 

[1]  1  6  8 10 12

sort(z, decreasing = TRUE)  

[1] 12 10  8  6  1

Malé cvičenie

w <- 5:36
sum(w[w %% 5 == 0])

[1] 140

---

Matice

Vytvorenie matíc

m <- matrix(1:12, nrow = 3, ncol = 4)            
m_byrow <- matrix(1:12, nrow = 3, byrow = TRUE)  
m; m_byrow

     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12
     [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12

Rozmery matice

dim(m)                   

[1] 3 4

m

     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12

Adresovanie prvkov matice

m[1, 2]      

[1] 4

m[ , 3]      

[1] 7 8 9

m[2, ]       

[1]  2  5  8 11

m[1:2, 2:3]  

     [,1] [,2]
[1,]    4    7
[2,]    5    8

Maticové operácie

A <- matrix(c(3,7,8,9), nrow = 2)
B <- matrix(c(5,6,7,8), nrow = 2)

A + B        # scitanie matic

     [,1] [,2]
[1,]    8   15
[2,]   13   17

A * B        # Hadamard product - nasobenie po zodpovedajucich prvkoch

     [,1] [,2]
[1,]   15   56
[2,]   42   72

A %*% B      # nasobenie matic

     [,1] [,2]
[1,]   63   85
[2,]   89  121

t(A)         # transpozicia matice A - vymena riadkov a stlpcov

     [,1] [,2]
[1,]    3    7
[2,]    8    9

det(A)       # determinant matice

[1] -29

solve(A)     # inverzia matice (ak je matica regularna - teda inverzia sa da spocitat)

           [,1]       [,2]
[1,] -0.3103448  0.2758621
[2,]  0.2413793 -0.1034483

Zlučovanie vektorov do matíc

C <- cbind(1:3, 4:6)   #  - po stlpcoch 
D <- rbind(1:3, 4:6)   #  - po riadkoch 
C; D

     [,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6

Vypočítanie zvolenej štatistiky po riadkoch (stĺpcoch) matice

M <- matrix(1:12, nrow = 3)
M

     [,1] [,2] [,3] [,4]
[1,]    1    4    7   10
[2,]    2    5    8   11
[3,]    3    6    9   12

apply(M, 1, sum)   # suma po riadkoch

[1] 22 26 30

apply(M, 2, mean)  # priemery po stĺpcoch

[1]  2  5  8 11

Malé cvičenie

M2 <- matrix(1:36, nrow = 6, byrow = TRUE)
colSums(M2)

[1]  96 102 108 114 120 126

t(M2) %*% M2

     [,1] [,2] [,3] [,4] [,5] [,6]
[1,] 2166 2262 2358 2454 2550 2646
[2,] 2262 2364 2466 2568 2670 2772
[3,] 2358 2466 2574 2682 2790 2898
[4,] 2454 2568 2682 2796 2910 3024
[5,] 2550 2670 2790 2910 3030 3150
[6,] 2646 2772 2898 3024 3150 3276

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